sprintf function

Write formatted data to string

Writes into the array pointed by str a C string consisting on a sequence of data formatted as the format argument specifies. After the format parameter, the function expects at least as many additional arguments as specified in format.
This function behaves exactly as printf does, but writing its results to a string instead of stdout. The size of the array passed as str should be enough to contain the entire formatted string.


Pointer to an array of char elements where the resulting C string is stored.
C string that contains the text to be written to the buffer.
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 number of format tags.
The format tags follow this prototype:

Where specifier is the most significant one and defines the type and the interpretation of the value of the coresponding argument:
d or iSigned decimal integer392
eScientific notation (mantise/exponent) using e character3.9265e+2
EScientific notation (mantise/exponent) using E character3.9265E+2
fDecimal floating point392.65
gUse the shorter of %e or %f392.65
GUse the shorter of %E or %f392.65
oSigned octal610
sString of characterssample
uUnsigned decimal integer7235
xUnsigned hexadecimal integer7fa
XUnsigned hexadecimal integer (capital letters)7FA
pPointer addressB800:0000
nNothing 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 % to the string.

The tag can also contain flags, width, .precision and modifiers sub-specifiers, which are optional and follow these specifications:

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.
0Left-pads the number with zeroes (0) instead of spaces, where padding is specified (see width sub-specifier).
*The width is not specified in the format string, but as an additional integer value argument preceding the argument thas has to be formatted.

For e, E and f specifiers: this is the number of digits to be printed after de decimal point.
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.
hThe argument is interpreted as 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.
LThe argument is interpreted as a long double (only applies to floating point specifiers: e, E, f, g and G).
additional arguments
Depending 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. There should be the same number of these arguments as the number of %-tags that expect a value.

Return Value

On failure, a negative number is returned.


/* sprintf example */

int main ()
char buffer [50];
int n, a=5, b=3;
printf ("[%s] is a %d char long string\n",buffer,n);
return 0;

[5 plus 3 is 8] is a 13 char long string