C Library Function - vsprintf()
C Standard Library - <stdio.h>
Description
The C library function int vsprintf(char *str, const char *format, va_list arg) sends formatted output to a string using an argument list.
Declaration
Here is the declaration for the vsprintf() function.
int vsprintf(char *str, const char *format, va_list arg)
Parameters
str -- This is a pointer to an array of chars where the resulting C string is stored.
format -- This is the string that contains the text to be written to the string. It can include embedded format tags that are replaced by values specified in subsequent additional arguments and formatted as requested. Format tags are %[flags][width][.precision][length]specifier, detailed as follows:
| Specifier | Output |
|---|---|
| c | Character |
| d or i | Signed decimal integer |
| e | Scientific notation (mantissa/exponent) using 'e' character |
| E | Scientific notation (mantissa/exponent) using 'E' character |
| f | Decimal floating point |
| g | Uses the shorter of %e or %f |
| G | Uses the shorter of %E or %f |
| o | Signed octal |
| s | String of characters |
| u | Unsigned decimal integer |
| x | Unsigned hexadecimal integer |
| X | Unsigned hexadecimal integer (uppercase) |
| p | Pointer address |
| n | Nothing printed |
| % | Character |
| Flags | Description |
|---|---|
| - | Left-justify within the given field width; right justification is the default (see width sub-specifier). |
| + | Forces to precede the result with a plus or minus sign (+ or -) even for positive numbers. By default, only negative numbers are preceded by 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 preceded with 0, 0x or 0X respectively for values 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 number 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 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 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 | Description |
|---|---|
| h | The argument is interpreted as a short int or unsigned short int (only applies to integer specifiers: i, d, o, u, x, X). |
| l | The argument is interpreted as a long int or unsigned long int for integer specifiers (i, d, o, u, x, X), and as a wide character or wide character string for specifiers c and s. |
| L | The argument is interpreted as a long double (applies only to floating-point specifiers: e, E, f, g, G). |
- arg -- A value representing a variable argument list, which should be initialized with the va_start macro defined in <stdarg>.
Return Value
On success, the total number of characters written is returned. On failure, a negative number is returned.
Example
The following example demonstrates the use of the vsprintf() function.
#include <stdio.h>
#include <stdarg.h>
char buffer[80];
int vspfunc(char *format, ...)
{
va_list aptr;
int ret;
va_start(aptr, format);
ret = vsprintf(buffer, format, aptr);
va_end(aptr);
return(ret);
}
int main()
{
int i = 5;
float f = 27.0;
char str[50] = "tutorialpro.org";
vspfunc("%d %f %s", i, f, str);
printf("%s\n", buffer);
return(0);
}
Let's compile and run the above program, which will produce the following result:
5 27.000000 tutorialpro.org