mirror of
https://github.com/golang/go
synced 2024-11-12 00:20:22 -07:00
fixups in the tutorial
also add a section about compiling programs because some found it surprising not to have one R=rsc CC=go-dev http://go/go-review/1018011
This commit is contained in:
Rob Pike
parent
dde666dab5
commit
83f0b718ed
@ -1,12 +1,15 @@
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<!-- Let's Go -->
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<h2>Introduction</h2>
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<p>
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This document is a tutorial introduction to the basics of the Go systems programming
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This document is a tutorial introduction to the basics of the Go programming
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language, intended for programmers familiar with C or C++. It is not a comprehensive
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guide to the language; at the moment the document closest to that is the
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<a href='/doc/go_spec.html'>language specification.</a>
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<a href='/doc/go_spec.html'>language specification</a>.
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After you've read this tutorial, you might want to look at
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<a href='/doc/effective_go.html'>Effective Go</a>,
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which digs deeper into how the language is used.
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<p>
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The presentation proceeds through a series of modest programs to illustrate
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The presentation here proceeds through a series of modest programs to illustrate
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key features of the language. All the programs work (at time of writing) and are
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checked into the repository in the directory <a href='/doc/progs'><code>/doc/progs/</code></a>.
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<p>
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@ -48,6 +51,35 @@ The comment convention is the same as in C++:
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<p>
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Later we'll have much more to say about printing.
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<p>
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<h2>Compiling</h2>
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<p>
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Go is a compiled language. At the moment there are two compilers.
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<code>Gccgo</code> is a Go compiler that uses the GCC back end. There is also a
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suite of compilers with different (and odd) names for each architecture:
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<code>6g</code> for the 64-bit x86, <code>8g</code> for the 32-bit x86, and more. These
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compilers run significantly faster but generate less efficient code
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than <code>gccgo</code>. At the time of writing (late 2009), they also have
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a more robust run-time system although <code>gccgo</code> is catching up.
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<p>
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Here's how to compile and run our program. With <code>6g</code>, say,
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<p>
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<pre>
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$ 6g helloworld.go # compile; object goes into helloworld.6
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$ 6l helloworld.6 # link; output goes into 6.out
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$ 6.out
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Hello, world; or Καλημέρα κόσμε; or こんにちは 世界
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$
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</pre>
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<p>
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With <code>gccgo</code> it looks a little more traditional.
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<p>
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<pre>
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$ gccgo helloworld.go
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$ a.out
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Hello, world; or Καλημέρα κόσμε; or こんにちは 世界
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$
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</pre>
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<p>
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<h2>Echo</h2>
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<p>
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Next up, here's a version of the Unix utility <code>echo(1)</code>:
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@ -63,8 +95,8 @@ Next up, here's a version of the Unix utility <code>echo(1)</code>:
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12 var n_flag = flag.Bool("n", false, "don't print final newline")
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<p>
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14 const (
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15 kSpace = " ";
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16 kNewline = "\n";
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15 Space = " ";
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16 Newline = "\n";
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17 )
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<p>
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19 func main() {
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@ -72,22 +104,22 @@ Next up, here's a version of the Unix utility <code>echo(1)</code>:
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21 var s string = "";
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22 for i := 0; i < flag.NArg(); i++ {
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23 if i > 0 {
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24 s += kSpace
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24 s += Space
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25 }
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26 s += flag.Arg(i)
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27 }
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28 if !*n_flag {
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29 s += kNewline
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29 s += Newline
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30 }
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31 os.Stdout.WriteString(s);
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32 }
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</pre>
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<p>
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This program is small but it's doing a number of new things. In the last example,
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we saw <code>func</code> introducing a function. The keywords <code>var</code>, <code>const</code>, and <code>type</code>
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we saw <code>func</code> introduce a function. The keywords <code>var</code>, <code>const</code>, and <code>type</code>
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(not used yet) also introduce declarations, as does <code>import</code>.
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Notice that we can group declarations of the same sort into
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parenthesized, semicolon-separated lists if we want, as on lines 4-10 and 14-17.
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parenthesized, semicolon-separated lists if we want, as on lines 7-10 and 14-17.
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But it's not necessary to do so; we could have said
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<p>
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<pre>
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@ -168,7 +200,7 @@ Later examples will show some other ways <code>for</code> can be written.
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<p>
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The body of the loop builds up the string <code>s</code> by appending (using <code>+=</code>)
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the flags and separating spaces. After the loop, if the <code>-n</code> flag is not
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set, it appends a newline, and then writes the result.
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set, the program appends a newline. Finally, it writes the result.
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<p>
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Notice that <code>main.main</code> is a niladic function with no return type.
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It's defined that way. Falling off the end of <code>main.main</code> means
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@ -234,7 +266,7 @@ about pointers to arrays.
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The size of the array is part of its type; however, one can declare
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a <i>slice</i> variable, to which one can assign a pointer to
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any array
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with the same element type or - much more commonly - a <i>slice
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with the same element type or—much more commonly—a <i>slice
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expression</i> of the form <code>a[low : high]</code>, representing
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the subarray indexed by <code>low</code> through <code>high-1</code>.
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Slices look a lot like arrays but have
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@ -276,7 +308,7 @@ and invoke it like this:
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Note how the return type (<code>int</code>) is defined for <code>sum()</code> by stating it
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after the parameter list.
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The expression <code>[3]int{1,2,3}</code> -- a type followed by a brace-bounded expression
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-- is a constructor for a value, in this case an array of 3 <code>ints</code>. Putting an <code>&</code>
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-- is a constructor for a value, in this case an array of 3 <code>ints</code>. Putting an <code>&</code>
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in front gives us the address of a unique instance of the value. We pass the
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pointer to <code>sum()</code> by (automatically) promoting it to a slice.
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<p>
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@ -288,7 +320,7 @@ elements for you, use <code>...</code> as the array size:
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</pre>
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<p>
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In practice, though, unless you're meticulous about storage layout within a
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data structure, a slice itself - using empty brackets and no <code>&</code> - is all you need:
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data structure, a slice itself - using empty brackets and no <code>&</code> - is all you need:
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<p>
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<pre>
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s := sum([]int{1,2,3});
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@ -297,7 +329,7 @@ data structure, a slice itself - using empty brackets and no <code>&</code> - is
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There are also maps, which you can initialize like this:
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<p>
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<pre>
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m := map[string] int {"one":1 , "two":2}
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m := map[string]int{"one":1 , "two":2}
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</pre>
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<p>
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The built-in function <code>len()</code>, which returns number of elements,
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@ -330,14 +362,14 @@ referencing the same underlying data will see the modification. For these three
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types you want to use the built-in function <code>make()</code>:
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<p>
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<pre>
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m := make(map[string] int);
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m := make(map[string]int);
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</pre>
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<p>
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This statement initializes a new map ready to store entries.
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If you just declare the map, as in
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<p>
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<pre>
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var m map[string] int;
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var m map[string]int;
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</pre>
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<p>
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it creates a <code>nil</code> reference that cannot hold anything. To use the map,
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@ -352,7 +384,7 @@ declaring an uninitialized variable and taking its address.
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<h2>An Interlude about Constants</h2>
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<p>
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Although integers come in lots of sizes in Go, integer constants do not.
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There are no constants like <code>0ll</code> or <code>0x0UL</code>. Instead, integer
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There are no constants like <code>0LL</code> or <code>0x0UL</code>. Instead, integer
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constants are evaluated as large-precision values that
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can overflow only when they are assigned to an integer variable with
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too little precision to represent the value.
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@ -394,7 +426,7 @@ sort of open/close/read/write interface. Here's the start of <code>file.go</cod
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10 )
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<p>
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12 type File struct {
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13 fd int; // file descriptor number
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13 fd int; // file descriptor number
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14 name string; // file name at Open time
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15 }
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</pre>
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@ -415,8 +447,8 @@ that the file descriptor refers to.
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<p>
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Because <code>File</code> starts with a capital letter, the type is available outside the package,
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that is, by users of the package. In Go the rule about visibility of information is
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simple: if a name (of a top-level type, function, method, constant, variable, or of
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a structure field) is capitalized, users of the package may see it. Otherwise, the
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simple: if a name (of a top-level type, function, method, constant or variable, or of
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a structure field or method) is capitalized, users of the package may see it. Otherwise, the
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name and hence the thing being named is visible only inside the package in which
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it is declared. This is more than a convention; the rule is enforced by the compiler.
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In Go, the term for publicly visible names is ''exported''.
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@ -545,7 +577,7 @@ the <code>struct</code> declaration itself. The <code>struct</code> declaration
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In fact, methods can be created for any type you name, such as an integer or
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array, not just for <code>structs</code>. We'll see an example with arrays later.
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<p>
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The <code>String</code> method is so called because of printing convention we'll
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The <code>String</code> method is so called because of a printing convention we'll
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describe later.
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<p>
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The methods use the public variable <code>os.EINVAL</code> to return the (<code>os.Error</code>
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@ -607,13 +639,13 @@ Building on the <code>file</code> package, here's a simple version of the Unix u
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17 for {
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18 switch nr, er := f.Read(&buf); true {
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19 case nr < 0:
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20 fmt.Fprintf(os.Stderr, "error reading from %s: %s\n", f.String(), er.String());
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20 fmt.Fprintf(os.Stderr, "cat: error reading from %s: %s\n", f.String(), er.String());
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21 os.Exit(1);
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22 case nr == 0: // EOF
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23 return;
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24 case nr > 0:
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25 if nw, ew := file.Stdout.Write(buf[0:nr]); nw != nr {
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26 fmt.Fprintf(os.Stderr, "error writing from %s: %s\n", f.String(), ew.String());
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26 fmt.Fprintf(os.Stderr, "cat: error writing from %s: %s\n", f.String(), ew.String());
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27 }
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28 }
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29 }
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@ -627,7 +659,7 @@ Building on the <code>file</code> package, here's a simple version of the Unix u
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37 for i := 0; i < flag.NArg(); i++ {
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38 f, err := file.Open(flag.Arg(i), 0, 0);
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39 if f == nil {
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40 fmt.Fprintf(os.Stderr, "can't open %s: error %s\n", flag.Arg(i), err);
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40 fmt.Fprintf(os.Stderr, "cat: can't open %s: error %s\n", flag.Arg(i), err);
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41 os.Exit(1);
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42 }
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43 cat(f);
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@ -702,7 +734,7 @@ we have a second implementation of the <code>reader</code> interface.
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50 // end of rotate13 implementation
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</pre>
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<p>
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(The <code>rot13</code> function called on line 42 is trivial and not worth reproducing.)
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(The <code>rot13</code> function called on line 42 is trivial and not worth reproducing here.)
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<p>
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To use the new feature, we define a flag:
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<p>
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@ -723,14 +755,14 @@ and use it from within a mostly unchanged <code>cat()</code> function:
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59 for {
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60 switch nr, er := r.Read(&buf); {
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61 case nr < 0:
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62 fmt.Fprintf(os.Stderr, "error reading from %s: %s\n", r.String(), er.String());
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62 fmt.Fprintf(os.Stderr, "cat: error reading from %s: %s\n", r.String(), er.String());
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63 os.Exit(1);
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64 case nr == 0: // EOF
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65 return;
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66 case nr > 0:
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67 nw, ew := file.Stdout.Write(buf[0:nr]);
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68 if nw != nr {
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69 fmt.Fprintf(os.Stderr, "error writing from %s: %s\n", r.String(), ew.String());
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69 fmt.Fprintf(os.Stderr, "cat: error writing from %s: %s\n", r.String(), ew.String());
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70 }
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71 }
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72 }
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@ -739,7 +771,7 @@ and use it from within a mostly unchanged <code>cat()</code> function:
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<p>
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(We could also do the wrapping in <code>main</code> and leave <code>cat()</code> mostly alone, except
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for changing the type of the argument; consider that an exercise.)
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Lines 56 through 59 set it all up: If the <code>rot13</code> flag is true, wrap the <code>reader</code>
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Lines 56 through 58 set it all up: If the <code>rot13</code> flag is true, wrap the <code>reader</code>
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we received into a <code>rotate13</code> and proceed. Note that the interface variables
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are values, not pointers: the argument is of type <code>reader</code>, not <code>*reader</code>,
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even though under the covers it holds a pointer to a <code>struct</code>.
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@ -838,8 +870,8 @@ to implement the three methods for that type, like this:
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<pre> <!-- progs/sortmain.go /type.day/ /Swap/ -->
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30 type day struct {
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31 num int;
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32 short_name string;
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33 long_name string;
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32 shortName string;
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33 longName string;
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34 }
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<p>
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36 type dayArray struct {
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@ -972,7 +1004,7 @@ Schematically, given a value <code>v</code>, it does this:
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if ok {
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result = s.String()
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} else {
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result = default_output(v)
|
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result = defaultOutput(v)
|
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}
|
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</pre>
|
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<p>
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@ -1002,7 +1034,7 @@ interface type defined in the <code>io</code> library:
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(This interface is another conventional name, this time for <code>Write</code>; there are also
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<code>io.Reader</code>, <code>io.ReadWriter</code>, and so on.)
|
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Thus you can call <code>Fprintf</code> on any type that implements a standard <code>Write()</code>
|
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method, not just files but also network channels, buffers, rot13ers, whatever
|
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method, not just files but also network channels, buffers, whatever
|
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you want.
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<p>
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<h2>Prime numbers</h2>
|
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@ -1010,7 +1042,10 @@ you want.
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Now we come to processes and communication -- concurrent programming.
|
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It's a big subject so to be brief we assume some familiarity with the topic.
|
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<p>
|
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A classic program in the style is the prime sieve of Eratosthenes.
|
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A classic program in the style is a prime sieve.
|
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(The sieve of Eratosthenes is computationationally more efficient than
|
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the algorithm presented here, but we are more interested in concurrency than
|
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algorithmics at the moment.)
|
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It works by taking a stream of all the natural numbers and introducing
|
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a sequence of filters, one for each prime, to winnow the multiples of
|
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that prime. At each step we have a sequence of filters of the primes
|
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@ -1310,6 +1345,3 @@ at the end of main:
|
||||
<p>
|
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There's a lot more to Go programming and concurrent programming in general but this
|
||||
quick tour should give you some of the basics.
|
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</table>
|
||||
</body>
|
||||
</html>
|
||||
|
||||
@ -2,12 +2,15 @@
|
||||
Introduction
|
||||
----
|
||||
|
||||
This document is a tutorial introduction to the basics of the Go systems programming
|
||||
This document is a tutorial introduction to the basics of the Go programming
|
||||
language, intended for programmers familiar with C or C++. It is not a comprehensive
|
||||
guide to the language; at the moment the document closest to that is the
|
||||
<a href='/doc/go_spec.html'>language specification.</a>
|
||||
<a href='/doc/go_spec.html'>language specification</a>.
|
||||
After you've read this tutorial, you might want to look at
|
||||
<a href='/doc/effective_go.html'>Effective Go</a>,
|
||||
which digs deeper into how the language is used.
|
||||
|
||||
The presentation proceeds through a series of modest programs to illustrate
|
||||
The presentation here proceeds through a series of modest programs to illustrate
|
||||
key features of the language. All the programs work (at time of writing) and are
|
||||
checked into the repository in the directory <a href='/doc/progs'>"/doc/progs/"</a>.
|
||||
|
||||
@ -40,6 +43,32 @@ The comment convention is the same as in C++:
|
||||
|
||||
Later we'll have much more to say about printing.
|
||||
|
||||
Compiling
|
||||
----
|
||||
|
||||
Go is a compiled language. At the moment there are two compilers.
|
||||
"Gccgo" is a Go compiler that uses the GCC back end. There is also a
|
||||
suite of compilers with different (and odd) names for each architecture:
|
||||
"6g" for the 64-bit x86, "8g" for the 32-bit x86, and more. These
|
||||
compilers run significantly faster but generate less efficient code
|
||||
than "gccgo". At the time of writing (late 2009), they also have
|
||||
a more robust run-time system although "gccgo" is catching up.
|
||||
|
||||
Here's how to compile and run our program. With "6g", say,
|
||||
|
||||
$ 6g helloworld.go # compile; object goes into helloworld.6
|
||||
$ 6l helloworld.6 # link; output goes into 6.out
|
||||
$ 6.out
|
||||
Hello, world; or Καλημέρα κόσμε; or こんにちは 世界
|
||||
$
|
||||
|
||||
With "gccgo" it looks a little more traditional.
|
||||
|
||||
$ gccgo helloworld.go
|
||||
$ a.out
|
||||
Hello, world; or Καλημέρα κόσμε; or こんにちは 世界
|
||||
$
|
||||
|
||||
Echo
|
||||
----
|
||||
|
||||
@ -48,10 +77,10 @@ Next up, here's a version of the Unix utility "echo(1)":
|
||||
--PROG progs/echo.go /package/ END
|
||||
|
||||
This program is small but it's doing a number of new things. In the last example,
|
||||
we saw "func" introducing a function. The keywords "var", "const", and "type"
|
||||
we saw "func" introduce a function. The keywords "var", "const", and "type"
|
||||
(not used yet) also introduce declarations, as does "import".
|
||||
Notice that we can group declarations of the same sort into
|
||||
parenthesized, semicolon-separated lists if we want, as on lines 4-10 and 14-17.
|
||||
parenthesized, semicolon-separated lists if we want, as on lines 7-10 and 14-17.
|
||||
But it's not necessary to do so; we could have said
|
||||
|
||||
const Space = " "
|
||||
@ -122,7 +151,7 @@ Later examples will show some other ways "for" can be written.
|
||||
|
||||
The body of the loop builds up the string "s" by appending (using "+=")
|
||||
the flags and separating spaces. After the loop, if the "-n" flag is not
|
||||
set, it appends a newline, and then writes the result.
|
||||
set, the program appends a newline. Finally, it writes the result.
|
||||
|
||||
Notice that "main.main" is a niladic function with no return type.
|
||||
It's defined that way. Falling off the end of "main.main" means
|
||||
@ -177,7 +206,7 @@ about pointers to arrays.
|
||||
The size of the array is part of its type; however, one can declare
|
||||
a <i>slice</i> variable, to which one can assign a pointer to
|
||||
any array
|
||||
with the same element type or - much more commonly - a <i>slice
|
||||
with the same element type or—much more commonly—a <i>slice
|
||||
expression</i> of the form "a[low : high]", representing
|
||||
the subarray indexed by "low" through "high-1".
|
||||
Slices look a lot like arrays but have
|
||||
@ -209,7 +238,7 @@ and invoke it like this:
|
||||
Note how the return type ("int") is defined for "sum()" by stating it
|
||||
after the parameter list.
|
||||
The expression "[3]int{1,2,3}" -- a type followed by a brace-bounded expression
|
||||
-- is a constructor for a value, in this case an array of 3 "ints". Putting an "&"
|
||||
-- is a constructor for a value, in this case an array of 3 "ints". Putting an "&"
|
||||
in front gives us the address of a unique instance of the value. We pass the
|
||||
pointer to "sum()" by (automatically) promoting it to a slice.
|
||||
|
||||
@ -219,13 +248,13 @@ elements for you, use "..." as the array size:
|
||||
s := sum(&[...]int{1,2,3});
|
||||
|
||||
In practice, though, unless you're meticulous about storage layout within a
|
||||
data structure, a slice itself - using empty brackets and no "&" - is all you need:
|
||||
data structure, a slice itself - using empty brackets and no "&" - is all you need:
|
||||
|
||||
s := sum([]int{1,2,3});
|
||||
|
||||
There are also maps, which you can initialize like this:
|
||||
|
||||
m := map[string] int {"one":1 , "two":2}
|
||||
m := map[string]int{"one":1 , "two":2}
|
||||
|
||||
The built-in function "len()", which returns number of elements,
|
||||
makes its first appearance in "sum". It works on strings, arrays,
|
||||
@ -253,12 +282,12 @@ If you're holding a slice or a map and you modify its contents, other variables
|
||||
referencing the same underlying data will see the modification. For these three
|
||||
types you want to use the built-in function "make()":
|
||||
|
||||
m := make(map[string] int);
|
||||
m := make(map[string]int);
|
||||
|
||||
This statement initializes a new map ready to store entries.
|
||||
If you just declare the map, as in
|
||||
|
||||
var m map[string] int;
|
||||
var m map[string]int;
|
||||
|
||||
it creates a "nil" reference that cannot hold anything. To use the map,
|
||||
you must first initialize the reference using "make()" or by assignment to an
|
||||
@ -273,7 +302,7 @@ An Interlude about Constants
|
||||
----
|
||||
|
||||
Although integers come in lots of sizes in Go, integer constants do not.
|
||||
There are no constants like "0ll" or "0x0UL". Instead, integer
|
||||
There are no constants like "0LL" or "0x0UL". Instead, integer
|
||||
constants are evaluated as large-precision values that
|
||||
can overflow only when they are assigned to an integer variable with
|
||||
too little precision to represent the value.
|
||||
@ -321,8 +350,8 @@ that the file descriptor refers to.
|
||||
|
||||
Because "File" starts with a capital letter, the type is available outside the package,
|
||||
that is, by users of the package. In Go the rule about visibility of information is
|
||||
simple: if a name (of a top-level type, function, method, constant, variable, or of
|
||||
a structure field) is capitalized, users of the package may see it. Otherwise, the
|
||||
simple: if a name (of a top-level type, function, method, constant or variable, or of
|
||||
a structure field or method) is capitalized, users of the package may see it. Otherwise, the
|
||||
name and hence the thing being named is visible only inside the package in which
|
||||
it is declared. This is more than a convention; the rule is enforced by the compiler.
|
||||
In Go, the term for publicly visible names is ''exported''.
|
||||
@ -390,7 +419,7 @@ the "struct" declaration itself. The "struct" declaration defines only data mem
|
||||
In fact, methods can be created for any type you name, such as an integer or
|
||||
array, not just for "structs". We'll see an example with arrays later.
|
||||
|
||||
The "String" method is so called because of printing convention we'll
|
||||
The "String" method is so called because of a printing convention we'll
|
||||
describe later.
|
||||
|
||||
The methods use the public variable "os.EINVAL" to return the ("os.Error"
|
||||
@ -459,7 +488,7 @@ we have a second implementation of the "reader" interface.
|
||||
|
||||
--PROG progs/cat_rot13.go /type.rotate13/ /end.of.rotate13/
|
||||
|
||||
(The "rot13" function called on line 42 is trivial and not worth reproducing.)
|
||||
(The "rot13" function called on line 42 is trivial and not worth reproducing here.)
|
||||
|
||||
To use the new feature, we define a flag:
|
||||
|
||||
@ -471,7 +500,7 @@ and use it from within a mostly unchanged "cat()" function:
|
||||
|
||||
(We could also do the wrapping in "main" and leave "cat()" mostly alone, except
|
||||
for changing the type of the argument; consider that an exercise.)
|
||||
Lines 56 through 59 set it all up: If the "rot13" flag is true, wrap the "reader"
|
||||
Lines 56 through 58 set it all up: If the "rot13" flag is true, wrap the "reader"
|
||||
we received into a "rotate13" and proceed. Note that the interface variables
|
||||
are values, not pointers: the argument is of type "reader", not "*reader",
|
||||
even though under the covers it holds a pointer to a "struct".
|
||||
@ -630,7 +659,7 @@ Schematically, given a value "v", it does this:
|
||||
if ok {
|
||||
result = s.String()
|
||||
} else {
|
||||
result = default_output(v)
|
||||
result = defaultOutput(v)
|
||||
}
|
||||
|
||||
The code uses a ``type assertion'' ("v.(Stringer)") to test if the value stored in
|
||||
@ -657,7 +686,7 @@ interface type defined in the "io" library:
|
||||
(This interface is another conventional name, this time for "Write"; there are also
|
||||
"io.Reader", "io.ReadWriter", and so on.)
|
||||
Thus you can call "Fprintf" on any type that implements a standard "Write()"
|
||||
method, not just files but also network channels, buffers, rot13ers, whatever
|
||||
method, not just files but also network channels, buffers, whatever
|
||||
you want.
|
||||
|
||||
Prime numbers
|
||||
@ -666,7 +695,10 @@ Prime numbers
|
||||
Now we come to processes and communication -- concurrent programming.
|
||||
It's a big subject so to be brief we assume some familiarity with the topic.
|
||||
|
||||
A classic program in the style is the prime sieve of Eratosthenes.
|
||||
A classic program in the style is a prime sieve.
|
||||
(The sieve of Eratosthenes is computationationally more efficient than
|
||||
the algorithm presented here, but we are more interested in concurrency than
|
||||
algorithmics at the moment.)
|
||||
It works by taking a stream of all the natural numbers and introducing
|
||||
a sequence of filters, one for each prime, to winnow the multiples of
|
||||
that prime. At each step we have a sequence of filters of the primes
|
||||
@ -825,6 +857,3 @@ at the end of main:
|
||||
|
||||
There's a lot more to Go programming and concurrent programming in general but this
|
||||
quick tour should give you some of the basics.
|
||||
</table>
|
||||
</body>
|
||||
</html>
|
||||
|
||||
@ -17,13 +17,13 @@ func cat(f *file.File) {
|
||||
for {
|
||||
switch nr, er := f.Read(&buf); true {
|
||||
case nr < 0:
|
||||
fmt.Fprintf(os.Stderr, "error reading from %s: %s\n", f.String(), er.String());
|
||||
fmt.Fprintf(os.Stderr, "cat: error reading from %s: %s\n", f.String(), er.String());
|
||||
os.Exit(1);
|
||||
case nr == 0: // EOF
|
||||
return;
|
||||
case nr > 0:
|
||||
if nw, ew := file.Stdout.Write(buf[0:nr]); nw != nr {
|
||||
fmt.Fprintf(os.Stderr, "error writing from %s: %s\n", f.String(), ew.String());
|
||||
fmt.Fprintf(os.Stderr, "cat: error writing from %s: %s\n", f.String(), ew.String());
|
||||
}
|
||||
}
|
||||
}
|
||||
@ -37,7 +37,7 @@ func main() {
|
||||
for i := 0; i < flag.NArg(); i++ {
|
||||
f, err := file.Open(flag.Arg(i), 0, 0);
|
||||
if f == nil {
|
||||
fmt.Fprintf(os.Stderr, "can't open %s: error %s\n", flag.Arg(i), err);
|
||||
fmt.Fprintf(os.Stderr, "cat: can't open %s: error %s\n", flag.Arg(i), err);
|
||||
os.Exit(1);
|
||||
}
|
||||
cat(f);
|
||||
|
||||
@ -59,14 +59,14 @@ func cat(r reader) {
|
||||
for {
|
||||
switch nr, er := r.Read(&buf); {
|
||||
case nr < 0:
|
||||
fmt.Fprintf(os.Stderr, "error reading from %s: %s\n", r.String(), er.String());
|
||||
fmt.Fprintf(os.Stderr, "cat: error reading from %s: %s\n", r.String(), er.String());
|
||||
os.Exit(1);
|
||||
case nr == 0: // EOF
|
||||
return;
|
||||
case nr > 0:
|
||||
nw, ew := file.Stdout.Write(buf[0:nr]);
|
||||
if nw != nr {
|
||||
fmt.Fprintf(os.Stderr, "error writing from %s: %s\n", r.String(), ew.String());
|
||||
fmt.Fprintf(os.Stderr, "cat: error writing from %s: %s\n", r.String(), ew.String());
|
||||
}
|
||||
}
|
||||
}
|
||||
@ -80,7 +80,7 @@ func main() {
|
||||
for i := 0; i < flag.NArg(); i++ {
|
||||
f, err := file.Open(flag.Arg(i), 0, 0);
|
||||
if f == nil {
|
||||
fmt.Fprintf(os.Stderr, "can't open %s: error %s\n", flag.Arg(i), err);
|
||||
fmt.Fprintf(os.Stderr, "cat: can't open %s: error %s\n", flag.Arg(i), err);
|
||||
os.Exit(1);
|
||||
}
|
||||
cat(f);
|
||||
|
||||
@ -12,8 +12,8 @@ import (
|
||||
var n_flag = flag.Bool("n", false, "don't print final newline")
|
||||
|
||||
const (
|
||||
kSpace = " ";
|
||||
kNewline = "\n";
|
||||
Space = " ";
|
||||
Newline = "\n";
|
||||
)
|
||||
|
||||
func main() {
|
||||
@ -21,12 +21,12 @@ func main() {
|
||||
var s string = "";
|
||||
for i := 0; i < flag.NArg(); i++ {
|
||||
if i > 0 {
|
||||
s += kSpace
|
||||
s += Space
|
||||
}
|
||||
s += flag.Arg(i)
|
||||
}
|
||||
if !*n_flag {
|
||||
s += kNewline
|
||||
s += Newline
|
||||
}
|
||||
os.Stdout.WriteString(s);
|
||||
}
|
||||
|
||||
@ -10,7 +10,7 @@ import (
|
||||
)
|
||||
|
||||
type File struct {
|
||||
fd int; // file descriptor number
|
||||
fd int; // file descriptor number
|
||||
name string; // file name at Open time
|
||||
}
|
||||
|
||||
|
||||
@ -29,8 +29,8 @@ func strings() {
|
||||
|
||||
type day struct {
|
||||
num int;
|
||||
short_name string;
|
||||
long_name string;
|
||||
shortName string;
|
||||
longName string;
|
||||
}
|
||||
|
||||
type dayArray struct {
|
||||
@ -56,7 +56,7 @@ func days() {
|
||||
panic()
|
||||
}
|
||||
for _, d := range data {
|
||||
fmt.Printf("%s ", d.long_name)
|
||||
fmt.Printf("%s ", d.longName)
|
||||
}
|
||||
fmt.Printf("\n")
|
||||
}
|
||||
|
||||
Loading…
Reference in New Issue
Block a user