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fmt: scanning widths apply after leading spaces

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When scanning with a width, as in %5s, C skips leading spaces
brefore counting the 5 characters. We should do the same.

Reword the documentation about widths to make this clear.

Fixes #9444

Change-Id: I443a6441adcf1c834057ef3977f9116a987a79cd
Reviewed-on: https://go-review.googlesource.com/10997
Reviewed-by: Andrew Gerrand <adg@golang.org>
This commit is contained in:
Rob Pike 2015-06-12 16:17:08 -07:00
parent ff8f3f0fa1
commit a1fe3b5046
3 changed files with 14 additions and 6 deletions
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17
src/fmt/doc.go
View File

@ -271,13 +271,18 @@
Flags # and + are not implemented.
The familiar base-setting prefixes 0 (octal) and 0x
(hexadecimal) are accepted when scanning integers without a
format or with the %v verb.
(hexadecimal) are accepted when scanning integers without
a format or with the %v verb.
Width is interpreted in the input text (%5s means at most
five runes of input will be read to scan a string) but there
is no syntax for scanning with a precision (no %5.2f, just
%5f).
Width is interpreted in the input text but there is no
syntax for scanning with a precision (no %5.2f, just %5f).
If width is provided, it applies after leading spaces are
trimmed and specifies the maximum number of runes to read
to satisfy the verb. For example,
Sscanf(" 1234567 ", "%5s%d", &s, &i)
will set s to "12345" and i to 67 while
Sscanf(" 12 34 567 ", "%5s%d", &s, &i)
will set s to "12" and i to 34.
In all the scanning functions, a carriage return followed
immediately by a newline is treated as a plain newline

1
src/fmt/scan.go
View File

@ -1165,6 +1165,7 @@ func (s *ss) doScanf(format string, a []interface{}) (numProcessed int, err erro
if !widPresent {
s.maxWid = hugeWid
}
s.SkipSpace()
s.argLimit = s.limit
if f := s.count + s.maxWid; f < s.argLimit {
s.argLimit = f

2
src/fmt/scan_test.go
View File

@ -340,6 +340,8 @@ var multiTests = []ScanfMultiTest{
{"%6vX=%3fY", "3+2iX=2.5Y", args(&c, &f), args((3 + 2i), 2.5), ""},
{"%d%s", "123abc", args(&i, &s), args(123, "abc"), ""},
{"%c%c%c", "2\u50c2X", args(&r1, &r2, &r3), args('2', '\u50c2', 'X'), ""},
{"%5s%d", " 1234567 ", args(&s, &i), args("12345", 67), ""},
{"%5s%d", " 12 34 567 ", args(&s, &i), args("12", 34), ""},
// Custom scanners.
{"%e%f", "eefffff", args(&x, &y), args(Xs("ee"), Xs("fffff")), ""},