Will the value of strlen("str") be evaluated at compile time or at runtime?

Question

C++ / C#

Will the code after compilation

int len = strlen("str");
int a = len + 1;
int b = len + 2;

equivalent to code

int a =  strlen("str") + 1;
int b =  strlen("str") + 2;

Answer 1

Absolutely not. But, if the compiler considers that your string does not change (and it does), it can optimize this code by replacing it with a constant. By the way, he can also throw out len, replacing it with a constant in the expressions below.
It is possible to say that it will surely replace only by knowing exactly which compiler is used and the compilation options.
gcc with -O3 100% will throw this line out and replace the expressions for a and b with a constant, but with -O0 it will most likely not touch it.
To make sure that the compiler does not optimize anything, you can use volatile, but in most cases there is no reason for this.

Answer 2

Unlikely.