C++ sprintf()

#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:

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