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fmt/Printf: document and tweak error messages produced for bad formats

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/2198044
This commit is contained in:
Rob Pike 2010-09-24 11:53:26 +10:00
parent d181625b9c
commit 344600f689
3 changed files with 42 additions and 21 deletions

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@ -69,8 +69,8 @@
Regardless of the verb, if an operand is an interface value,
the internal concrete value is used, not the interface itself.
Thus:
var i interface{} = 23;
fmt.Printf("%v\n", i);
var i interface{} = 23
fmt.Printf("%v\n", i)
will print 23.
If an operand implements interface Formatter, that interface
@ -85,6 +85,26 @@
cast the value before recurring:
func (x X) String() string { return Sprintf("%d", int(x)) }
Format errors:
If an invalid argument is given for a verb, such as providing
a string to %d, the generated string will contain a
description of the problem, as in these examples:
Wrong type or unknown verb: %!verb(type=value)
Printf("%d", hi): %!d(string=hi)
Too many arguments: %!(EXTRA type=value)
Printf("hi", "guys"): hi%!(EXTRA string=guys)
Too few arguments: %!verb(MISSING)
Printf("hi%d"): hi %!d(MISSING)
Non-int for width or precision: %!(BADWIDTH) or %!(BADPREC)
Printf("%*s", 4.5, "hi"): %!(BADWIDTH)hi
Printf("%.*s", 4.5, "hi"): %!(BADPREC)hi
All errors begin with the string "%!" followed sometimes
by a single character (the verb) and end with a parenthesized
description.
Scanning:
An analogous set of functions scans formatted text to yield
@ -97,7 +117,7 @@
routines treat newlines as spaces.
Scanf, Fscanf, and Sscanf parse the arguments according to a
format string, analogous to that of Printf. For example, "%x"
format string, analogous to that of Printf. For example, %x
will scan an integer as a hexadecimal number, and %v will scan
the default representation format for the value.

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@ -193,8 +193,8 @@ var fmttests = []fmtTest{
fmtTest{"%+.3g", complex128(1 + 2i), "(+1+2i)"},
// erroneous formats
fmtTest{"", 2, "?(extra int=2)"},
fmtTest{"%d", "hello", "%d(string=hello)"},
fmtTest{"", 2, "%!(EXTRA int=2)"},
fmtTest{"%d", "hello", "%!d(string=hello)"},
// old test/fmt_test.go
fmtTest{"%d", 1234, "1234"},
@ -301,7 +301,7 @@ var fmttests = []fmtTest{
fmtTest{"%s", I(23), `<23>`},
fmtTest{"%q", I(23), `"<23>"`},
fmtTest{"%x", I(23), `3c32333e`},
fmtTest{"%d", I(23), `%d(string=<23>)`},
fmtTest{"%d", I(23), `%!d(string=<23>)`},
// go syntax
fmtTest{"%#v", A{1, 2, "a", []int{1, 2}}, `fmt_test.A{i:1, j:0x2, s:"a", x:[]int{1, 2}}`},
@ -321,7 +321,7 @@ var fmttests = []fmtTest{
// renamings
fmtTest{"%v", renamedBool(true), "true"},
fmtTest{"%d", renamedBool(true), "%d(fmt_test.renamedBool=true)"},
fmtTest{"%d", renamedBool(true), "%!d(fmt_test.renamedBool=true)"},
fmtTest{"%o", renamedInt(8), "10"},
fmtTest{"%d", renamedInt8(-9), "-9"},
fmtTest{"%v", renamedInt16(10), "10"},
@ -366,14 +366,14 @@ var fmttests = []fmtTest{
fmtTest{"%p", make(chan int), "PTR"},
fmtTest{"%p", make(map[int]int), "PTR"},
fmtTest{"%p", make([]int, 1), "PTR"},
fmtTest{"%p", 27, "%p(int=27)"}, // not a pointer at all
fmtTest{"%p", 27, "%!p(int=27)"}, // not a pointer at all
// erroneous things
fmtTest{"%d", "hello", "%d(string=hello)"},
fmtTest{"no args", "hello", "no args?(extra string=hello)"},
fmtTest{"%s", nil, "%s(<nil>)"},
fmtTest{"%d", "hello", "%!d(string=hello)"},
fmtTest{"no args", "hello", "no args%!(EXTRA string=hello)"},
fmtTest{"%s", nil, "%!s(<nil>)"},
fmtTest{"%T", nil, "<nil>"},
fmtTest{"%-1", 100, "%1(int=100)"},
fmtTest{"%-1", 100, "%!1(int=100)"},
}
func TestSprintf(t *testing.T) {
@ -622,12 +622,12 @@ var startests = []starTest{
starTest{"%-*d", args(4, 42), "42 "},
// erroneous
starTest{"%*d", args(nil, 42), "%(badwidth)42"},
starTest{"%.*d", args(nil, 42), "%(badprec)42"},
starTest{"%*d", args(5, "foo"), "%d(string= foo)"},
starTest{"%*d", args(nil, 42), "%!(BADWIDTH)42"},
starTest{"%.*d", args(nil, 42), "%!(BADPREC)42"},
starTest{"%*d", args(5, "foo"), "%!d(string= foo)"},
starTest{"%*% %d", args(20, 5), "% 5"},
starTest{"%*", args(4), "%(badwidth)%*(int=4)"},
starTest{"%*d", args(int32(4), 42), "%(badwidth)42"},
starTest{"%*", args(4), "%!(BADWIDTH)%!*(int=4)"},
starTest{"%*d", args(int32(4), 42), "%!(BADWIDTH)42"},
}
// TODO: there's no conversion from []T to ...T, but we can fake it. These

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@ -20,12 +20,12 @@ var (
nilParenBytes = []byte("(nil)")
nilBytes = []byte("nil")
mapBytes = []byte("map[")
missingBytes = []byte("missing")
extraBytes = []byte("?(extra ")
missingBytes = []byte("(MISSING)")
extraBytes = []byte("%!(EXTRA ")
irparenBytes = []byte("i)")
bytesBytes = []byte("[]byte{")
widthBytes = []byte("%(badwidth)")
precBytes = []byte("%(badprec)")
widthBytes = []byte("%!(BADWIDTH)")
precBytes = []byte("%!(BADPREC)")
)
// State represents the printer state passed to custom formatters.
@ -266,6 +266,7 @@ func (p *pp) unknownType(v interface{}) {
func (p *pp) badVerb(verb int, val interface{}) {
p.add('%')
p.add('!')
p.add(verb)
p.add('(')
if val == nil {