C++ sprintf()

The sprintf() function in C++ is used to write a formatted string to character string buffer. It is defined in the cstdio header file.

Example

#include <cstdio>
#include <iostream>
using namespace std;

int main() {
  char buffer[100];
  int age = 23;

// print "My age is " and age variable to buffer variable sprintf(buffer, "My age is %d", age);
// print buffer variable cout << buffer; return 0; } // Output: My age is 23

sprintf() Syntax

The syntax of sprintf() is:

sprintf(char* buffer, const char* format, ...);

Here,

  • buffer is the string buffer to which we need to write
  • format is the string that is to be written to the string buffer
  • ... in the above code signifies you can pass more than one argument to sprintf().

sprintf() Parameters

The sprintf() function takes the following parameters:

  • buffer - pointer to the string buffer to write the result.
  • format - pointer to a null-terminated string (C-string) that is written to the string buffer. It consists of characters along with optional format specifiers starting with %.
  • ... - other additional arguments specifying the data to be printed. They occur in a sequence according to the format specifier.

sprintf() Return Value

The sprintf() function returns:

  • On Success - the number of characters written for sufficiently large buffer (excluding the terminating null character '\0')
  • On failure - a negative value

sprintf() Prototype

The prototype of the sprintf() function as defined in the cstdio header file is:

int sprintf(char* buffer, const char* format, ...);

Format Specifier

The format parameter of printf() can contain format specifiers that begin with %. These specifiers are replaced by the values of respective variables that follow the format string.

A format specifier has the following parts:

  • A leading % sign
  • flags - one or more flags that modifies the conversion behavior (optional)
    • - : Left justify the result within the field. By default it is right justified.
    • + : The sign of the result is attached to the beginning of the value, even for positive results.
    • space: If there is no sign, a space is attached to the beginning of the result.
    • # : An alternative form of the conversion is performed.
    • 0 : It is used for integer and floating point numbers. Leading zeros are used to pad the numbers instead of space.
  • width - an optional * or integer value used to specify minimum width field.
  • precision - an optional field consisting of a . followed by * or integer or nothing to specify the precision.
  • length - an optional length modifier that specifies the size of the argument.
  • specifier - a conversion format specifier.

sprintf() Format Specifier Prototype

The general prototype of format specifier for sprintf() is:

%[flags][width][.precision][length]specifier

Commonly Used Format Specifiers

The table below lists some commonly used format specifiers:

Format Specifier Description
% a % followed by another % character prints % to the screen
c writes a single character
s writes a character string
d or i converts a signed integer to decimal representation
o converts an unsigned integer to octal representation
X or x converts an unsigned integer to hexadecimal representation
u converts an unsigned integer to decimal representation
F or f converts floating-point number to the decimal representation
E or e converts floating-point number to the decimal exponent notation
A or a converts floating-point number to the hexadecimal exponent
G or g converts floating-point number to either decimal or decimal exponent notation
n - returns the number of characters written so far
- the result is written to the value pointed to by the argument
- the argument must be a pointer to signed int
p writes an implementation-defined character sequence defining a pointer

Example: C++ sprintf()

#include <cstdio>
#include <iostream>
using namespace std;

int main() {
  char buffer[100];
  int count;
  char name[] = "Max";
  int age = 23;

// write combination of strings and variables to buffer variable // store the number of characters written in count count = sprintf(buffer, "Hi, I am %s and I am %d years old", name, age);
// print the string buffer cout << buffer << endl; // print the number of characters written cout << "Number of characters written = " << count; return 0; }

Output

Hi, I am Max and I am 23 years old
Number of characters written = 34

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