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doc: update format for "C? Go? Cgo!" article

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CC=golang-dev
https://golang.org/cl/5841050
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Shenghou Ma 2012-03-19 22:54:06 +08:00
parent 2ef4a84022
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2 changed files with 30 additions and 31 deletions
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59
doc/articles/c_go_cgo.html
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@ -22,24 +22,24 @@ Let’s look at what's happening here, starting with the import statement.
</p>
<p>
The rand package imports "C", but you'll find there's no such package in
the standard Go library. That's because <code>C</code> is a
The <code>rand</code> package imports <code>"C"</code>, but you'll find there's
no such package in the standard Go library. That's because <code>C</code> is a
"pseudo-package", a special name interpreted by cgo as a reference to C's
name space.
</p>
<p>
The rand package contains four references to the <code>C</code> package:
the calls to <code>C.random</code> and <code>C.srandom</code>, the
conversion <code>C.uint(i)</code>, and the import statement.
The <code>rand</code> package contains four references to the <code>C</code>
package: the calls to <code>C.random</code> and <code>C.srandom</code>, the
conversion <code>C.uint(i)</code>, and the <code>import</code> statement.
</p>
<p>
The <code>Random</code> function calls the libc random function and returns
the result. In C, random returns a value of the C type <code>long</code>,
which cgo represents as the type <code>C.long</code>. It must be converted
to a Go type before it can be used by Go code outside this package, using
an ordinary Go type conversion:
The <code>Random</code> function calls the standard C library's <code>random</code>
function and returns the result. In C, <code>random</code> returns a value of the
C type <code>long</code>, which cgo represents as the type <code>C.long</code>.
It must be converted to a Go type before it can be used by Go code outside this
package, using an ordinary Go type conversion:
</p>
{{code "/doc/progs/cgo1.go" `/func Random/` `/STOP/`}}
@ -54,30 +54,30 @@ the type conversion more explicitly:
<p>
The <code>Seed</code> function does the reverse, in a way. It takes a
regular Go <code>int</code>, converts it to the C <code>unsigned int</code>
type, and passes it to the C function srandom.
type, and passes it to the C function <code>srandom</code>.
</p>
{{code "/doc/progs/cgo1.go" `/func Seed/` `/END/`}}
<p>
Note that cgo knows the unsigned int type as C.uint; see the
<a href="/cmd/cgo">cgo documentation</a> for a complete list of these
numeric type names.
Note that cgo knows the <code>unsigned int</code> type as <code>C.uint</code>;
see the <a href="/cmd/cgo">cgo documentation</a> for a complete list of
these numeric type names.
</p>
<p>
The one detail of this example we haven't examined yet is the comment
above the import statement.
above the <code>import</code> statement.
</p>
{{code "/doc/progs/cgo1.go" `/INCLUDE/` `/STOP/`}}
{{code "/doc/progs/cgo1.go" `/\/\*/` `/STOP/`}}
<p>
Cgo recognizes this comment and uses it as a header when compiling the C
parts of the package. In this case it is just a simple include statement,
but it can be any valid C code. The comment must be immediately before the
line that imports "C", without any intervening blank lines, just like a
documentation comment.
line that imports <code>"C"</code>, without any intervening blank lines,
just like a documentation comment.
</p>
<p>
@ -114,11 +114,11 @@ by calling <code>C.free</code>.
<p>
The call to <code>C.CString</code> returns a pointer to the start of the
char array, so before the function exits we convert it to an
<a href="/pkg/unsafe/#Pointer">unsafe.Pointer</a> and release the memory
allocation with <code>C.free</code>. A common idiom in cgo programs is to
<a href="/doc/articles/defer_panic_recover.html">defer</a> the free
immediately after allocating (especially when the code that follows is more
complex than a single function call), as in this rewrite of
<a href="/pkg/unsafe/#Pointer"><code>unsafe.Pointer</code></a> and release
the memory allocation with <code>C.free</code>. A common idiom in cgo programs
is to <a href="/doc/articles/defer_panic_recover.html"><code>defer</code></a>
the free immediately after allocating (especially when the code that follows
is more complex than a single function call), as in this rewrite of
<code>Print</code>:
</p>
@ -129,10 +129,11 @@ complex than a single function call), as in this rewrite of
</p>
<p>
To build cgo packages, just use <a href="/cmd/go/#Compile_packages_and_dependencies">"go build"</a> or
<a href="/cmd/go/#Compile_and_install_packages_and_dependencies">"go install"</a>
as usual. The go tool recognizes the special "C" import and automatically uses
cgo for those files.
To build cgo packages, just use <a href="/cmd/go/#Compile_packages_and_dependencies">"
<code>go build</code>"</a> or
<a href="/cmd/go/#Compile_and_install_packages_and_dependencies">"<code>go install</code>
"</a> as usual. The go tool recognizes the special <code>"C"</code> import and automatically
uses cgo for those files.
</p>
<p>
@ -141,8 +142,8 @@ cgo for those files.
<p>
The <a href="/cmd/cgo/">cgo command</a> documentation has more detail about
the C pseudo-package and the build process. The cgo examples in the Go tree
demonstrate more advanced concepts.
the C pseudo-package and the build process. The <a href="/misc/cgo/">cgo examples</a>
in the Go tree demonstrate more advanced concepts.
</p>
<p>

2
doc/progs/cgo1.go
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@ -3,8 +3,6 @@
// license that can be found in the LICENSE file.
package rand
// INCLUDE OMIT
/*
#include <stdlib.h>
*/