function_printf.doc

1、functionprintfint printf ( const char * format, . );Print formatted data to stdoutWrites to the standard output (stdout) a sequence of data formatted as the format argument specifies. After theformat parameter, the function expects at least as many additional arguments as specified in format.Paramet

2、ersformatString that contains the text to be written to stdout.It can optionally contain embedded format tags that are substituted by the values specified in subsequent argument(s) and formatted as requested.The number of arguments following the format parameters should at least be as much as the nu

3、mber of format tags.The format tags follow this prototype:%flagswidth.precisionlengthspecifier Where specifier is the most significant one and defines the type and the interpretation of the value of the coresponding argument:specifier OutputExamplec Character ad or i Signed decimal integer 392e Scie

4、ntific notation (mantissa/exponent) using e character 3.9265e+2E Scientific notation (mantissa/exponent) using E character 3.9265E+2f Decimal floating point 392.65g Use the shorter of %e or %f 392.65G Use the shorter of %E or %f 392.65o Unsigned octal 610s String of characters sampleu Unsigned decim

5、al integer 7235x Unsigned hexadecimal integer 7faX Unsigned hexadecimal integer (capital letters) 7FAp Pointer address B800:0000n Nothing printed. The argument must be a pointer to a signed int, where the number of characters written so far is stored.% A % followed by another % character will write

6、% to stdout. %The tag can also contain flags, width, .precision and length sub-specifiers, which are optional and follow these specifications:flags description- Left-justify within the given field width; Right justification is the default (see width sub-specifier).+ Forces to precede the result with

7、 a plus or minus sign (+ or -) even for positive numbers. By default, only negative numbers are preceded with a - sign.(space) If no sign is going to be written, a blank space is inserted before the value.#Used with o, x or X specifiers the value is preceeded with 0, 0x or 0X respectively for values

8、 different than zero.Used with e, E and f, it forces the written output to contain a decimal point even if no digits would follow. By default, if no digits follow, no decimal point is written.Used with g or G the result is the same as with e or E but trailing zeros are not removed.0 Left-pads the nu

9、mber with zeroes (0) instead of spaces, where padding is specified (see width sub-specifier).width description(number)Minimum number of characters to be printed. If the value to be printed is shorter than this number, the result is padded with blank spaces. The value is not truncated even if the res

10、ult is larger.* The width is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.precision description.numberFor integer specifiers (d, i, o, u, x, X): precision specifies the minimum number of digits to be written. If the v

11、alue to be written is shorter than this number, the result is padded with leading zeros. The value is not truncated even if the result is longer. A precision of 0 means that no character is written for the value 0.For e, E and f specifiers: this is the number of digits to be printed after the decima

12、l point.For g and G specifiers: This is the maximum number of significant digits to be printed.For s: this is the maximum number of characters to be printed. By default all characters are printed until the ending null character is encountered.For c type: it has no effect.When no precision is specifi

13、ed, the default is 1. If the period is specified without an explicit value for precision, 0 is assumed.* The precision is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.length descriptionh The argument is interpreted as

14、 a short int or unsigned short int (only applies to integer specifiers: i,d, o, u, x and X).lThe argument is interpreted as a long int or unsigned long int for integer specifiers (i, d, o, u, x and X), and as a wide character or wide character string for specifiers c and s.L The argument is interpre

15、ted as a long double (only applies to floating point specifiers: e, E, f, g and G).additional argumentsDepending on the format string, the function may expect a sequence of additional arguments, each containing one value to be inserted instead of each %-tag specified in the format parameter, if any.

16、 There should be the same number of these arguments as the number of %-tags that expect a value.Return ValueOn success, the total number of characters written is returned.On failure, a negative number is returned.Example123456789101112/* printf example */#include int main()printf (“Characters: %c %c

17、 n“, a, 65);printf (“Decimals: %d %ldn“, 1977, 650000L);printf (“Preceding with blanks: %10d n“, 1977);printf (“Preceding with zeros: %010d n“, 1977);printf (“Some different radixes: %d %x %o %#x %#o n“, 100, 100, 100, 100, 100);printf (“floats: %4.2f %+.0e %E n“, 3.1416, 3.1416, 3.1416);printf (“Width trick: %*d n“, 5, 10);printf (“%s n“, “A string“);return 0;And here is the output:Characters: a ADecimals: 1977 650000Preceding with blanks: 1977Preceding with zeros: 0000001977Some different radixes: 100 64 144 0x64 0144floats: 3.14 +3e+000 3.141600E+000Width trick: 10A string