Dynamic arrays in C without malloc?

Question

I\'ve always wondered how I could get away with this:

int main(int argc, char **argv) {
    printf(\"%p %s %d\\n\", &argv[1], argv[1], strlen(argv[1]));
         


        

Answer 1

"Variable length arrays" were added to the C language in C99. This is covered in §6.7.5.2 "Array declarators":

If the size is an expression that is not an integer constant expression: if it occurs in a declaration at function prototype scope, it is treated as if it were replaced by *; otherwise, each time it is evaluated it shall have a value greater than zero. The size of each instance of a variable length array type does not change during its lifetime. Where a size expression is part of the operand of a sizeof operator and changing the value of the size expression would not affect the result of the operator, it is unspecified whether or not the size expression is evaluated.