What are the C library functions?

Library functions are built-in functions that are grouped together and placed in a common location called library. Each function performs a specific operation, allowing us to get pre-defined outputs without implementing complex logic from scratch.

All C standard library functions are declared by using many header files. These library functions are created at the time of designing the compilers.

We include the header files in our C program by using #include<filename.h>. Whenever the program is compiled and executed, the related files are included in the C program.

Syntax

#include <header_file.h>

int main() {
    // Use library functions here
    return 0;
}

Common Header Files

Here are the most commonly used header files in C programming −

• stdio.h − Standard input/output header file where I/O functions are declared

• string.h − All string manipulation functions are in this header file

• stdlib.h − Contains general utility functions like memory allocation, process control

• math.h − All mathematical functions like sin(), cos(), sqrt() are declared here

• time.h − Contains time and date manipulation functions

Example: Using Library Functions

Here's a simple program demonstrating the use of various library functions −

#include <stdio.h>
#include <string.h>
#include <math.h>

int main() {
    char name[50] = "TutorialsPoint";
    int length;
    double result;
    
    // Using stdio.h functions
    printf("Website: %s<br>", name);
    
    // Using string.h functions
    length = strlen(name);
    printf("Length: %d<br>", length);
    
    // Using math.h functions
    result = sqrt(25.0);
    printf("Square root of 25: %.2f<br>", result);
    
    return 0;
}

Website: TutorialsPoint
Length: 14
Square root of 25: 5.00

Key stdio.h Functions

The stdio.h header contains essential input/output functions. Here are the most commonly used ones −

Conclusion

C library functions provide pre-written, tested code for common programming tasks. Using appropriate header files like stdio.h, string.h, and math.h saves development time and ensures reliability in your programs.