const char * vs const char ** on argv

Question

I want to get a filename from a commandline argument so I can pass it to a file-opening function, however, argv[] seems to be of type const char ** by default, even if it was defined as "const char * argv[]" in the main's arguments. My function requires const char *, is there a way to convert this two, or something?

int main(int argc, const char *argv[]) {
    memory Memory;
    Memory.loadROM(argv); // Error 'argument of type "const char **" is incompatible with parameter of type "const char *"'
}

Answer 1

When used in function parameters without being a reference type, const char *argv[] and const char **argv is exactly identical because the former will be adjusted to the latter.

Per N4296, Section 8.3.5p5:

any parameter of type “array of T” or “function returning T” is adjusted to be “pointer to T” or “pointer to function returning T,” respectively

So const char *argv[] is "an array of type const char * " and is thus adjusted to "a pointer to const char * ".

And since argv is of type const char ** , you want to dereference it to get a const char * :

Memory.loadROM(argv[1])

Answer 2

argv contains an array of char * , so if you only want one, simplify specify which you want:

Memory.loadROM(argv[1]);

Read here for more on what'll be in argv .

Answer 3

The difference between char* argv[] and char** argv is actually pretty subtle, so you'll often see them used interchangeably. The typical default is char** argv since that's more conventional, yet the alternative isn't wrong.

In both cases argv[0] is the first argument. Remember that pointers act like arrays and char* argv[] is an array of char* .