Restrict keyword in C

The restrict keyword in C is a type qualifier that informs the compiler that a pointer is the only reference to an object during its lifetime.

This helps the compiler in making certain optimizations to potentially improve performance.

The restrict keyword restricts a pointer to be the sole means to access the data it points to within its scope.

This enables the compiler to optimize the code more aggressively by making assumptions about pointer aliasing.

Syntax:

type * restrict pointer_name;

Example:

// program for restrict in C
#include<stdio.h> 

void copy_data(int A, int * restrict dest, const int * restrict src) {
    for (int i = 0; i < A; i++) {
        dest[i] = src[i];
    }
}

int main() {
    int source[5] = {1, 2, 3, 4, 5};
    int destination[5];

    copy_data(5, destination, source);

    printf("Copied data:\n");
    for (int i = 0; i < 5; i++) {
        printf("%d ", destination[i]);
    }
    printf("\n");

    return 0;
}

Output:

Copied data:
1 2 3 4 5

Key Points:

Optimization: The restrict keyword helps the compiler optimize code by making assumptions about pointer aliasing.

Single Reference: It indicates that the pointer is the sole reference to an object within its scope.

Performance: Use of restrict can lead to performance improvements in scenarios where the compiler can optimize more aggressively.

Understanding the restrict keyword and its implications can be beneficial for optimizing performance-critical sections of your C code.