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I am trying to compare the parameter of command with argv[] but it's not working. Here is my code.
./a.out -d 1
In main function
int main (int argc, char * const argv[]) {
if (argv[1] == "-d")
// call some function here
}
But this is not working... I don't know why this comparison is not working.
488
argv is an array of pointers to characters.
char** argv is the same as char* argv[] because in the second case "the name of the array is a pointer to the first element in the array".
The first parameter, argc (argument count) is an integer that indicates how many arguments were entered on the command line when the program was started. The second parameter, argv (argument vector), is an array of pointers to arrays of character objects.
The second argument to main, usually called argv, is an array of strings. A string is just an array of characters, so argv is an array of arrays. There are standard C functions that manipulate strings, so it's not too important to understand the details of argv, as long as you see a few examples of using it.
You can't compare strings using ==. Instead, use strcmp.
#include <string.h>
int main (int argc, char * const argv[]) {
if (strcmp(argv[1], "-d") == 0)
// call some function here
}
The reason for this is that the value of "..." is a pointer representing the location of the first character in the string, with the rest of the characters after it. When you specify "-d" in your code, it makes a whole new string in memory. Since the location of the new string and argv[1] aren't the same, == will return 0.
70
In C++ let std::string do the work for you:
#include <string>
int main (int argc, char * const argv[]) {
if (argv[1] == std::string("-d"))
// call some function here
}
In C you'll have to use strcmp:
if (strcmp(argv[1], "-d") == 0)
// call some function here
}
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