Thread: Making a const char * out of argv

  1. #1
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    Making a const char * out of argv

    Hello, everyone. Here is the barebones of my code. I am trying to iterate the strings pointed to by argv, to parse options etc. My code never modifies the argv array, nor the strings pointed to by it, and I want the compiler to enforce that (and to provide an optimization hint to the compiler).

    Code:
    void fn(int argc, const char *argv[])
    {
    }
    
    int main(int argc, char *argv[])
    {
      fn(argc, argv);
    }
    This compiles with gcc 5.4.0 with a warning:

    Code:
    test.c: In function ‘main’:
    test.c:7:12: warning: passing argument 2 of ‘fn’ from incompatible pointer type [-Wincompatible-pointer-types]
       fn(argc, argv);
                ^
    test.c:1:6: note: expected ‘const char **’ but argument is of type ‘char **’
     void fn(int argc, const char *argv[])
    I can use (const char **) when passing argv, but that feels like a sledgehammer that can mask problems. What's the correct solution?

    Richard

  2. #2
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    Question 11.10

    The "solution" is to use the cast.

  3. #3
    Programming Wraith GReaper's Avatar
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    Quote Originally Posted by Richardcavell View Post
    I can use (const char **) when passing argv, but that feels like a sledgehammer that can mask problems. What's the correct solution?
    That's strange, the compiler shouldn't complain about implicit casting from pointer to const pointer... Well, I guess the way to be rid of that warning is to either explicitly disable it or cast the pointer to const.

    EDIT: Oh, as I see at that page, a double pointer is treated differently.
    Last edited by GReaper; 08-10-2017 at 01:21 PM.
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