diff options
Diffstat (limited to 'src/pkg/fmt/doc.go')
| -rw-r--r-- | src/pkg/fmt/doc.go | 35 |
1 files changed, 23 insertions, 12 deletions
diff --git a/src/pkg/fmt/doc.go b/src/pkg/fmt/doc.go index 35a11e19f..9660370c2 100644 --- a/src/pkg/fmt/doc.go +++ b/src/pkg/fmt/doc.go @@ -7,7 +7,8 @@ to C's printf and scanf. The format 'verbs' are derived from C's but are simpler. - Printing: + + Printing The verbs: @@ -30,8 +31,9 @@ %X base 16, with upper-case letters for A-F %U Unicode format: U+1234; same as "U+%04X" Floating-point and complex constituents: - %b decimalless scientific notation with exponent a power - of two, in the manner of strconv.Ftoa32, e.g. -123456p-78 + %b decimalless scientific notation with exponent a power of two, + in the manner of strconv.FormatFloat with the 'b' format, + e.g. -123456p-78 %e scientific notation, e.g. -1234.456e+78 %E scientific notation, e.g. -1234.456E+78 %f decimal point but no exponent, e.g. 123.456 @@ -89,14 +91,22 @@ If an operand implements interface Formatter, that interface can be used for fine control of formatting. - If an operand implements method String() string that method + If the format (which is implicitly %v for Println etc.) is valid + for a string (%s %q %v %x %X), the following two rules also apply: + + 1. If an operand implements the error interface, the Error method + will be used to convert the object to a string, which will then + be formatted as required by the verb (if any). + + 2. If an operand implements method String() string, that method will be used to convert the object to a string, which will then - be formatted as required by the verb (if any). To avoid - recursion in cases such as - type X int - func (x X) String() string { return Sprintf("%d", x) } - cast the value before recurring: - func (x X) String() string { return Sprintf("%d", int(x)) } + be formatted as required by the verb (if any). + + To avoid recursion in cases such as + type X string + func (x X) String() string { return Sprintf("<%s>", x) } + convert the value before recurring: + func (x X) String() string { return Sprintf("<%s>", string(x)) } Format errors: @@ -118,11 +128,12 @@ by a single character (the verb) and end with a parenthesized description. - Scanning: + + Scanning An analogous set of functions scans formatted text to yield values. Scan, Scanf and Scanln read from os.Stdin; Fscan, - Fscanf and Fscanln read from a specified os.Reader; Sscan, + Fscanf and Fscanln read from a specified io.Reader; Sscan, Sscanf and Sscanln read from an argument string. Scanln, Fscanln and Sscanln stop scanning at a newline and require that the items be followed by one; Sscanf, Fscanf and Sscanf require |