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How do I detect the user passed no arguments to a program with getopt_long? I could detect the user calling the program with no arguments by checking argc, but what about the user calling my program with just a dash?

$ my_prog -

Do I need to include this option somehow in my getopt statement?

while(ca = getopt_long(argc, argv, "abc:D:",...)

What would the function return?

blackscreen1
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2 Answers2

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You can use optind variable to determine such arguments:

The variable optind is the index of the next element of the argv[] vector to be processed. It shall be initialized to 1 by the system, and getopt() shall update it when it finishes with each element of argv[].

For example,

  for(int i = optind; i < argc; i++)
    printf("Unknown argument: %s\n", argv[i]);

You can do this after argument processing to find out if there are any such unexpected arguments.

P.P
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Just start your optstring with '-' character. From man getopt_long:

If the first character of optstring is '-', then each nonoption argv-element is handled as if it were the argument of an option with character code 1

So with the optstring "-abc:D:" you can assume there were some arguments passed if you entered the while loop.

nsilent22
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