Does Declaring Loop Variables in C Impact Performance?

Loop Variable Declaration Overhead

In C , it's often debated whether declaring a variable within a loop impacts performance. Consider the following scenario:

int i = 0;
while (i < 100) {
    int var = 4;
    i++;
}

Here, int var is declared within the loop and is assigned the value 4 every iteration. It may seem that this repetitive declaration would introduce overhead. However, in C , local variables are typically allocated on the stack within the function's scope.

int i = 0;
int var;
while (i < 100) {
    var = 4;
    i++;
}

In this case, int var is declared outside the loop to eliminate potential overhead. However, both snippets behave identically speed and efficiency-wise.

The reason for this is that the stack space for local variables is allocated at the beginning of the function's scope. In this example, the stack space for int var is allocated when the function starts, regardless of whether it's declared within or outside the loop. Therefore, the only overhead involved is the assignment of 4 to var during each iteration.

The above is the detailed content of Does Declaring Loop Variables in C Impact Performance?. For more information, please follow other related articles on the PHP Chinese website!