A flag directive is a character that specifies output justification and output of signs, blanks, leading zeros, decimal points, and octal and hexadecimal prefixes. More than one flag directive may appear in a format specification, and flags can appear in any order.
| Flag | Meaning | Default |
|---|---|---|
| - | Left align the result within the given field width. | Right align. |
| + | Use a sign (+ or –) to prefix the output value if it is of a signed type. | Sign appears only for negative signed values (–). |
| blank (' ') | Use a blank to prefix the output value if it is signed and positive. The blank is ignored if both the blank and + flags appear. | No blank appears. |
| # | When it's used with the o format, the # flag uses 0 to prefix any nonzero output value. | |
| When it's used with the x, or X format, the # flag uses 0x, or 0X, respectively, to prefix any nonzero output value. | ||
| When it's used with the e, E, f, a or A format, the # flag forces the output value to contain a decimal point. | Decimal point appears only if digits follow it. | |
| When it's used with the g or G format, the # flag forces the output value to contain a decimal point and prevents the truncation of trailing zeros. Ignored when used with c, d, i, u, or s. | Decimal point appears only if digits follow it. Trailing zeros are truncated. | |
| 0 | If width is prefixed by 0, leading zeros are added until the minimum width is reached. If both 0 and – appear, the 0 is ignored. If 0 is specified as an integer format (i, u, x, X, o, d) and a precision specification is also present—for example, %04.d—the 0 is ignored. | No padding. |
The plus sign (+) takes precedence over the space if both are used.