In this guide, you will learn what is fprintf() function is in C++ programming and how to use it with an example.

1. fprintf() Function Overview

The fprintf() function is part of the <cstdio> library in C++. It allows for formatted output to a specified stream, most commonly used for writing formatted strings to files. It is analogous to the printf() function, but instead of writing to the standard output, it writes to a given file stream.

Signature:

int fprintf(FILE* stream, const char* format, ...);

Parameters:

- stream: Pointer to the file stream where the formatted output should be written.

- format: A string that specifies how the subsequent arguments are converted for output.

- ...: Variable number of arguments that will be formatted and printed according to the format string.

2. Source Code Example

#include <iostream> #include <cstdio> int main() { FILE* pFile = fopen("example.txt", "w"); if (pFile == nullptr) { std::cerr << "Error opening file." << std::endl; return 1; } // Write formatted data to the file int age = 25; const char* name = "John Doe"; fprintf(pFile, "Name: %s\nAge: %d", name, age); // Close the file fclose(pFile); std::cout << "Data written to the file successfully." << std::endl; return 0; } 

Output:

Data written to the file successfully. (Note: An "example.txt" file will be created with the content: Name: John Doe Age: 25 ) 

3. Explanation

1. We first open a file named "example.txt" in write mode.

2. The fprintf() function is then used to write a formatted string to the pFile stream. The %s format specifier is replaced by the string name, and the %d format specifier is replaced by the integer age.

3. Finally, the file is closed using fclose().