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Defining own main functions arguments argc and argv

Asked 2009-10-05T12:47:06.590
31

i want to create an object of type QApplication which needs the main functions arguments argc and argv as an input:

QApplication app(argc, argv);

Since i am within a user defined function without access to the main function i want to define this arguments on my own. I have tried several approaches but i cannot get the type conversion right. My last approach did not work either:

int argc = 1;
char **argv; 
char arguments[1][12] = {{"cgalExample"}};
argv = arguments;

Thanks for any hint.

c++ qt
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1 Answer

45

If you want to be insanely pendantic, then you want something like the following. The key points are that argv is not const, argv is NULL terminated, argc is the number of usable elements in argv including the program name. It is required to be modifiable so you cannot use string literals - argv[i] is required to point to a modifiable array of characters.

int my_main() {
    char  arg0[] = "programName";
    char  arg1[] = "arg";
    char  arg2[] = "another arg";
    char* argv[] = { &arg0[0], &arg1[0], &arg2[0], NULL };
    int   argc   = (int)(sizeof(argv) / sizeof(argv[0])) - 1;

    QApplication the_application(argc, &argv[0]);
    return the_application.run();
}

The Standard (ISO/IEC 9899:1999 section 5.1.2.2.1) states that the following is true about argc and argv in a hosted environment:

  • The value of argc shall be nonnegative.
  • argv[argc] shall be a null pointer.
  • If the value of argc is greater than zero, the array members argv[0] through argv[argc-1] inclusive shall contain pointers to strings, which are given implementation-defined values by the host environment prior to program startup from elsewhere in the hosted environment. If the host environment is not capable of supplying strings with letters in both uppercase and lowercase, the implementation shall ensure that the strings are received in lowercase.
  • If the value of argc is greater than zero, the string pointed to by argv[0] represents the program name; argv[0][0] shall be the null character if the program name is not available fro
answered 2009-10-05T13:11:54.607

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