The old code put the index before the period in the precision;
it should be after so it's always before the star, as documented.
A little trickier to do in one pass but compensated for by more
tests and catching a couple of other error cases.
R=rsc
CC=golang-dev
https://golang.org/cl/9751044
This text is added to doc.go:
Explicit argument indexes:
In Printf, Sprintf, and Fprintf, the default behavior is for each
formatting verb to format successive arguments passed in the call.
However, the notation [n] immediately before the verb indicates that the
nth one-indexed argument is to be formatted instead. The same notation
before a '*' for a width or precision selects the argument index holding
the value. After processing a bracketed expression [n], arguments n+1,
n+2, etc. will be processed unless otherwise directed.
For example,
fmt.Sprintf("%[2]d %[1]d\n", 11, 22)
will yield "22, 11", while
fmt.Sprintf("%[3]*[2].*[1]f", 12.0, 2, 6),
equivalent to
fmt.Sprintf("%6.2f", 12.0),
will yield " 12.00". Because an explicit index affects subsequent verbs,
this notation can be used to print the same values multiple times
by resetting the index for the first argument to be repeated:
fmt.Sprintf("%d %d %#[1]x %#x", 16, 17)
will yield "16 17 0x10 0x11".
The notation chosen differs from that in C, but I believe it's easier to read
and to remember (we're indexing the arguments), and compatibility with
C's printf was never a strong goal anyway.
While we're here, change the word "field" to "arg" or "argument" in the
code; it was being misused and was confusing.
R=rsc, bradfitz, rogpeppe, minux.ma, peter.armitage
CC=golang-dev
https://golang.org/cl/9680043
This CL also replaces similar loops in other stdlib
package tests with calls to AllocsPerRun.
Fixes#4461.
R=minux.ma, rsc
CC=golang-dev
https://golang.org/cl/7002055
Silly and small but easy to be consistent.
To make it worthwhile, I eliminated an allocation when using
%x on a byte slice.
Fixes#4149.
R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6574046
Before, pointers always appeared as 0x1234ABCD. This CL
keeps that as the default for %p and %v, but lets explicit
numeric verbs override the default.
Fixes#3936.
R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/6441152
The reordering speedup in CL 6245068 changed the semantics
of %#v by delaying the clearing of some flags. Restore the old
semantics and add a test.
Fixes#3706.
R=golang-dev, r
CC=golang-dev
https://golang.org/cl/6302048
The check for Stringer etc. can only fire if the test is not a builtin, so avoid
the expensive check if we know there's no chance.
Also put in a fast path for pad, which saves a more modest amount.
benchmark old ns/op new ns/op delta
BenchmarkSprintfEmpty 148 152 +2.70%
BenchmarkSprintfString 585 497 -15.04%
BenchmarkSprintfInt 441 396 -10.20%
BenchmarkSprintfIntInt 718 603 -16.02%
BenchmarkSprintfPrefixedInt 676 621 -8.14%
BenchmarkSprintfFloat 1003 953 -4.99%
BenchmarkManyArgs 2945 2312 -21.49%
BenchmarkScanInts 1704152 1734441 +1.78%
BenchmarkScanRecursiveInt 1837397 1828920 -0.46%
R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/6245068
Unexports runtime.MemStats and rename MemStatsType to MemStats.
The new accessor requires passing a pointer to a user-allocated
MemStats structure.
Fixes#2572.
R=bradfitz, rsc, bradfitz, gustavo
CC=golang-dev, remy
https://golang.org/cl/5616072
We need to avoid allocating an extra word for the interface value
passing the floating-point value as an interface{}. It's easy.
Fixes#2722.
R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/5553044
On 32-bit machines, %g takes an extra malloc. I don't know why yet,
but this makes the test pass again, and enables it even for -short.
Fixes#2653.
R=golang-dev, bradfitz, r
CC=golang-dev
https://golang.org/cl/5542055
This is a slight change to fmt's semantics, but means that if you use
%d to print an integer with a Stringable value, it will print as an integer.
This came up because Time.Month() couldn't cleanly print as an integer
rather than a name. Using %d on Stringables is silly anyway, so there
should be no effect outside the fmt tests.
As a mild bonus, certain recursive failures of String methods
will also be avoided this way.
R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/5453053
Got rid of all the magic mystery globals. Now
for %N, %T, and %S, the flags +,- and # set a sticky
debug, sym and export mode, only visible in the new fmt.c.
Default is error mode. Handle h and l flags consistently with
the least side effects, so we can now change
things without worrying about unrelated things
breaking.
fixes#2361
R=rsc
CC=golang-dev
https://golang.org/cl/5316043
Had been allowing it for use by fmt, but it is too hard to lock down.
Fix other packages not to depend on it.
R=r, r
CC=golang-dev
https://golang.org/cl/5266054
Interesting that Fprintf can do zero mallocs.
(Sprintf must allocate the returned string.)
R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/4977049
The C-stdlib heritage of printf/fprintf/sprintf has two odd
aspects for precisions of zero with integers. First, the zero
can be specified in any of these ways, "%4.0d", "%.0d" and
"%.d" which was not previously supported here. Secondly, the
seemingly universal interpretation of precision for integers
is that precision==0 and value==0 means print nothing at all.
The code here now handles this for integers just as the code
in big/int.c does the same for the Int type. New tests are
added to fmt_test.go to verify these changes.
R=r, r
CC=golang-dev
https://golang.org/cl/4717045
This change causes Print et al. to catch panics generated by
calls to String, GoString, and Format. The panic is formatted
into the output stream as an error, but the program continues.
As a special case, if the argument was a nil pointer, the
result is just "<nil>", because that's almost certainly enough
information and handles the very common case of String
methods that don't guard against nil.
Scan does not want this change. Input must work; output can
be for debugging and it's nice to get output even when you
make a mistake.
R=dsymonds, r, adg, gri, rsc, gri
CC=golang-dev
https://golang.org/cl/4640043
%+q uses strconv.Quote[Rune]ToASCII, guaranteeing ASCII-only output.
%#U a quoted character if the rune is printable: 'x'=U+0078; otherwise
it's as before: U+000A.
R=golang-dev, gri, rsc
CC=golang-dev
https://golang.org/cl/4589047
add QuoteToASCII.
The Quote and QuoteRune functions now let printable
runes (as defined by unicode.IsPrint) through. When
true 7-bit clean stuff is necessary, there are now two
new functions: QuoteToASCII and QuoteRuneToASCII.
Printf("%q") uses Quote. To get the old behavior, it
will now be necessary to say
Printf("%s", strconv.QuoteToASCII(s))
but that should rarely be necessary.
R=golang-dev, gri, r
CC=golang-dev
https://golang.org/cl/4561061
Also fix a bug: precision was in terms of bytes; should be runes.
Fixes#1652.
R=rsc, bradfitzgo, r2, bradfitzwork
CC=golang-dev
https://golang.org/cl/4280086