diff options
Diffstat (limited to 'src/pkg/fmt/doc.go')
| -rw-r--r-- | src/pkg/fmt/doc.go | 33 |
1 files changed, 31 insertions, 2 deletions
diff --git a/src/pkg/fmt/doc.go b/src/pkg/fmt/doc.go index b8dd995c7..095fd03b2 100644 --- a/src/pkg/fmt/doc.go +++ b/src/pkg/fmt/doc.go @@ -118,6 +118,28 @@ convert the value before recurring: func (x X) String() string { return Sprintf("<%s>", string(x)) } + 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". + Format errors: If an invalid argument is given for a verb, such as providing @@ -133,6 +155,9 @@ Non-int for width or precision: %!(BADWIDTH) or %!(BADPREC) Printf("%*s", 4.5, "hi"): %!(BADWIDTH)hi Printf("%.*s", 4.5, "hi"): %!(BADPREC)hi + Invalid or invalid use of argument index: %!(BADINDEX) + Printf("%*[2]d", 7): %!d(BADINDEX) + Printf("%.[2]d", 7): %!d(BADINDEX) All errors begin with the string "%!" followed sometimes by a single character (the verb) and end with a parenthesized @@ -144,9 +169,9 @@ through the fmt package. For example, if a String method calls panic("bad"), the resulting formatted message will look like - %s(PANIC=bad) + %!s(PANIC=bad) - The %s just shows the print verb in use when the failure + The %!s just shows the print verb in use when the failure occurred. Scanning @@ -190,6 +215,10 @@ stops if it does not, with the return value of the function indicating the number of arguments scanned. + In all the scanning functions, a carriage return followed + immediately by a newline is treated as a plain newline + (\r\n means the same as \n). + In all the scanning functions, if an operand implements method Scan (that is, it implements the Scanner interface) that method will be used to scan the text for that operand. Also, |