Question

I’m studying linux C++ programing when I see

int execve(const char *path,
           char *const argv[],
           char *const envp[]);

I don’t understand what is char *const argv[] . I know char *const foo is a const pointer to char. And const char *foo is a pointer to a const char. But what’s char *const argv[]?

Is it an array of const pointers to char or an array of pointers to const char?

And I have a vector<string> now, how to convert it to char *const argv[]?

Answer 1

Is it an array of const pointers to char or an array of pointers to const char?

Read types right to left:
const always binds to the left (unless it is on the very left)

char *const argv[]

                ^^ Array of
      ^^^^^        const
     ^             pointer to
^^^^               char

An array of "const pointer" to char

So the pointers in the array can not be modified.
But what they point at can be modified.

Note: As pointed out by Steve below. Because this is being used as a parameter. It actually decays to a “A pointer to "const pointer" to char” or “char* const *”.

And I have a vector<string> now, how to convert it to char *const argv[]?

int execve(const char *path,
       char *const argv[],
       char *const envp[]);

int main()
{
    std::vector<std::string>   data;  /// fill
    std::vector<char*>         argv;
    std::vector<char*>         envp;

    for(std::vector<std::string>::iterator loop = data.begin(); loop != data.end(); ++loop)
    {
        argv.push_back(&(*loop)[0]);
    }

    // I also bet that argv and envp need to be NULL terminated
    argv.push_back(NULL);
    envp.push_back(NULL);
    execve("MyAppName", &argv[0], &envp[0]);
}