Will strlen be calculated multiple times if used in a loop condition?

Question

I\'m not sure if the following code can cause redundant calculations, or is it compiler-specific?

for (int i = 0; i < strlen(ss); ++i)
{
    // blabla
}
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Answer 1

Yes, every time you use the loop. Then it will every time calculate the length of the string. so use it like this:

char str[30];
for ( int i = 0; str[i] != '\0'; i++)
{
//Something;
}

In the above code str[i] only verifies one particular character in the string at location i each time the loop starts a cycle, thus it will take less memory and is more efficient.

See this Link for more information.

In the code below every time the loop runs strlen will count the length of the whole string which is less efficient, takes more time and takes more memory.

char str[];
for ( int i = 0; i < strlen(str); i++)
{
//Something;
}

Answer 2

Yes, the strlen() function is called every time the loop is evaluated.

If you want to improve the efficiency then always remember to save everything in local variables... It will take time but it's very useful ..

You can use code like below:

String str="ss";
int l = strlen(str);

for ( int i = 0; i < l ; i++ )
{
    // blablabla
}

Answer 3

Yes, the strlen(ss) will calculate the length at each iteration. If you are increasing the ss by some way and also increasing the i; there would be infinite loop.

Answer 4

Yes, strlen() will be evaluated on each iteration. It's possible that, under ideal circumstances, the optimiser might be able to deduce that the value won't change, but I personally wouldn't rely on that.

I'd do something like

for (int i = 0, n = strlen(ss); i < n; ++i)

or possibly

for (int i = 0; ss[i]; ++i)

as long as the string isn't going to change length during the iteration. If it might, then you'll need to either call strlen() each time, or handle it through more complicated logic.

Answer 5

Yes.

strlen() calculated everytime when i increases and does not optimized.

Below code shows why the compiler should not optimize strlen().

for ( int i = 0; i < strlen(ss); ++i )
{
   // Change ss string.
   ss[i] = 'a'; // Compiler should not optimize strlen().
}

Answer 6

Yes, strlen(ss) will be calculated every time the code runs.