printf 用法

format

C string that contains the text to be written to stdout.
It can optionally contain embedded format specifiers that are replaced by the values specified in subsequent additional arguments and formatted as requested.

A format specifier follows this prototype: [see compatibility note below] 
%[flags][width][.precision][length]specifier 

Where the specifier character at the end is the most significant component, since it defines the type and the interpretation of its corresponding argument:
specifierOutputExampled or iSigned decimal integer392uUnsigned decimal integer7235oUnsigned octal610xUnsigned hexadecimal integer7faXUnsigned hexadecimal integer (uppercase)7FAfDecimal floating point, lowercase392.65FDecimal floating point, uppercase392.65eScientific notation (mantissa/exponent), lowercase3.9265e+2EScientific notation (mantissa/exponent), uppercase3.9265E+2gUse the shortest representation: %e or %f392.65GUse the shortest representation: %E or %F392.65aHexadecimal floating point, lowercase-0xc.90fep-2AHexadecimal floating point, uppercase-0XC.90FEP-2cCharacterasString of characterssamplepPointer addressb8000000nNothing printed.
The corresponding argument must be a pointer to a signed int.
The number of characters written so far is stored in the pointed location. %A % followed by another % character will write a single % to the stream.%
The format specifier can also contain sub-specifiers: flags, width, .precision and modifiers (in that order), which are optional and follow these specifications:

flagsdescription-Left-justify within the given field width; Right justification is the default (see width sub-specifier).+Forces to preceed the result with 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 different than zero.
Used with a, A, e, E, f, F, g or G it forces the written output to contain a decimal point even if no more digits follow. By default, if no digits follow, no decimal point is written.0Left-pads the number with zeroes (0) instead of spaces when padding is specified (see width sub-specifier).
widthdescription(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 result 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.
.precisiondescription.numberFor integer specifiers (d, i, o, u, x, X): precision specifies the minimum number of digits to be written. If the value 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 a, A, e, E, f and F specifiers: this is the number of digits to be printed after the decimal 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.
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.
The length sub-specifier modifies the length of the data type. This is a chart showing the types used to interpret the corresponding arguments with and without length specifier (if a different type is used, the proper type promotion or conversion is performed, if allowed):
 specifierslengthd iu o x Xf F e E g G a Acspn(none)intunsigned intdoubleintchar*void*int*hhsigned charunsigned char    signed char*hshort intunsigned short int    short int*llong intunsigned long int wint_twchar_t* long int*lllong long intunsigned long long int    long long int*jintmax_tuintmax_t    intmax_t*zsize_tsize_t    size_t*tptrdiff_tptrdiff_t    ptrdiff_t*L  long double    Note that the c specifier takes an int (or wint_t) as argument, but performs the proper conversion to a charvalue (or a wchar_t) before formatting it for output.

Note: Yellow rows indicate specifiers and sub-specifiers introduced by C99.

... (additional arguments)

Depending on the format string, the function may expect a sequence of additional arguments, each containing a value to be used to replace a format specifier in the format string (or a pointer to a storage location, for n).
There should be at least as many of these arguments as the number of values specified in the format specifiers. Additional arguments are ignored by the function.

Return Value

On success, the total number of characters written is returned.

If a writing error occurs, the error indicator (ferror) is set and a negative number is returned.

If a multibyte character encoding error occurs while writing wide characters, errno is set to EILSEQ and a negative number is returned.

Example

123456789101112131415

/* printf example */#include <stdio.h>int main(){   printf ("Characters: %c %c \n", 'a', 65);   printf ("Decimals: %d %ld\n", 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;}

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