Cant Workout Why this C Condition Fails

I have a problem with some C code I am writing as part of a University assignment. Consider the code:

printf("%s\n", argv[1]);
if ((argv[1] == "--verbose") || (argv[1] == "-v")) {
  printf("%d\n", argc);
}

now: printf("%s\n", argv[1]); prints "--verbose" so I know 开发者_如何学编程argv[1] == "--verbose" should be true, but the line printf("%d\n", argc); never executes. And I cant workout why. Any ideas?

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Use the strcmp function:

strcmp(argv[1], "--verbose") == 0

== checks that two pointers have the same address, which is not what you want.

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Refer to Wikipedia Article on strcmp.

Key here is you cannot compare strings directly with the == operator in C. This will only compare the pointers to the strings, which will be different.

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Because you can't compare strings with == in C. Use strcmp or similar.

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Shouldn't you be using strcmp to compare strings? Surely argv[1] == "--verbose" will not compare for equality of the strings to the letter.

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In your code you are actually comparing the contents of the argv[1] pointer (which points to the string containing the first argument of your program) with the address of each string literal ("-v" etc). This is guaranteed to be false in all cases.

You should use the strcmp() function or similar to compare the strings themselves, rather than their addresses.