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[ C Standard Library - ](#) ## Description The C library function **int vfprintf(FILE *stream, const char *format, va_list arg)** sends formatted output to a stream using an argument list. ## Declaration The following is the declaration for the vfprintf() function. ```c int vfprintf(FILE *stream, const char *format, va_list arg) ## Parameters * **stream** -- This is a pointer to a FILE object that identifies the stream. * **format** -- This is a C string containing the text to be written to the stream. It can optionally contain embedded format tags that are replaced by the values specified in subsequent additional arguments and formatted as requested. The format tags follow this prototype: **%[.precision]specifier**, explained below: | specifier | Output | | --- | --- | | c | Character | | d or i | Signed decimal integer | | e | Scientific notation using e character (mantissa and exponent) | | E | Scientific notation using E character (mantissa and exponent) | | f | Decimal floating point | | g | Uses the shorter of %e or %f | | G | Uses the shorter of %E or %f | | o | Unsigned octal | | s | String of characters | | u | Unsigned decimal integer | | x | Unsigned hexadecimal integer | | X | Unsigned hexadecimal integer (uppercase) | | p | Pointer address | | n | No output | | % | Character | | flags | Description | | --- | --- | | - | Left-align within the given field width, right alignment is the default (see width sub-specifier). | | + | Forces to precede the result with a plus or minus sign (+ or -), i.e., positive numbers will display a + sign. By default, only negative numbers are preceded with a - sign. | | (space) | Inserts a blank space before the value if no sign is going to be written. | | # | Used with o, x or X specifiers the value is preceded with 0, 0x or 0X respectively for non-zero values. Used with e, E and f it forces the output to contain a decimal point, even if no more digits 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 number with zeroes (0) instead of spaces when 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 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. | | .precision | Description | | --- | --- | | .number | For 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 e, E 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. For c type: it has no effect. When no precision is specified, the default is 1. If the period is specified without an explicit value, 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 | Description | | --- | --- | | h | The argument is interpreted as a short int or unsigned short int (only applies to integer specifiers: i, d, o, u, x and X). | | l | The 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 interpreted as a long double (only applies to floating point specifiers: e, E, f, g and G). | * **arg** -- An object representing the variable argument list. This should be initialized by the va_start macro defined in . ## Return Value If successful, returns the total number of characters written, otherwise a negative number is returned. ## Example The following example demonstrates the usage of the vfprintf() function. ```c #include #include void WriteFrmtd(FILE *stream, char *format, ...) { va_list args; va_start(args, format); vfprintf(stream, format, args); va_end(args); } int main () { FILE *fp; fp = fopen("file.txt","w"); WriteFrmtd(fp, "This is just one argument %d n", 10); fclose(fp); return(0); } Let's compile and run the above program, which will open the file **file.txt** in the current directory and write the following content: This is just one argument 10 Now let's use the following program to view the contents of the above file: ```c #include int main () { FILE *fp; int c; fp = fopen("file.txt","r"); while(1) { c = fgetc(fp); if( feof(fp) ) { break ; } printf("%c", c); } fclose(fp); return(0); } [ C Standard Library - ](#)