[C++] Command Line Arguments help

Hello CProgrammers,

I have been struggling all afternoon trying to bring a resolution to this issue.

Application: Calculator

Issue: Command Line Arguments
When the user gets to the command line and enters the file name and switch the program doesn't read the switch properly. The source code is below. When it reads the switch, even if it is correct, it doesn't perform the correct operation. I believe it isn't reading the switch right.

Basically when the program reads the switch, it doesn't do the code i've asked it to. Example: If (a = "-m") { do this } else { do that } and even if it should be the first if block, it does the else.

The area i'm having trouble with is colored in red.

[View full source code]

Code:

int main(int sizeOfArrayV, char *switches[]) { // This application will accept switches for (int x = 0; x < sizeOfArrayV; x++) { cout << "Switch #" << x << " =: " << switches[x] << endl; } cout << endl; if(switches[1]) { // If switches 1 is defined: if(switches[1] == "-m" || switches[1] == "-M") { // error handling cout << "Multiple variables... [ENABLED!]" << endl; } else if(switches[1] == "-x" || switches[1] == "-X") { // The user did not enter the switch: cout << "Multiple variables... [DISABLED!]" << endl; } else { // The user did not enter '-x' or '-m'. cout << "You must enter a proper value! Please enter '-x' to disable the switch!" << endl; } } else { // The user must enter -m or -x because if they don't the order will be messed up. // This will be called if the user simply clicks the '.exe' instead of using the CL. cout << "Switches... [DISABLED!]" << endl; }

[View full source code]

Thanks,
-camelCase

You can't use your own names for command line arguments. It's int argc (for argument count), char *argv[] (for argument vector). argv is an array of strings. The text the user types to execute the program from the command line is argv[0]. Every argument after that is argv[1], argv[2], and so on.

I don't think there is much harm in using one's own names.
Anyway, the problem is, once again, the C backwards compatibility. You cannot compare string literals that way.
The best and easiest way to solve it is to wrap the command arguments inside std::strings.
Eg:

Code:

std::string Args[] = { std::string(switches[0]), std::string(switches[1]), ... };

Then you can compare them the way you do.

Well if all he needs to do is compare them, then std::strcmp works as well. The cost is one more header, #include <cstring>. I think the effort to make them std::string arrays is only worth it if you need to edit the arguments themselves.

Quote:

Originally Posted by Elysia

I don't think there is much harm in using one's own names.
Anyway, the problem is, once again, the C backwards compatibility. You cannot compare string literals that way.
The best and easiest way to solve it is to wrap the command arguments inside std::strings.
Eg:

Code:

std::string Args[] = { std::string(switches[0]), std::string(switches[1]), ... };

Then you can compare them the way you do.

I kind of understand what you're implementing but I don't fully understand. I've created a variable called 'switches' with type std::string. I compare statements to this variable though it does the same thing.

I'm actually losing track of what you mean.

From what I can see, switches is created as a parameter to main; its type being

char *switches[]

C string arrays and std::string arrays are not the same.

I stand by my earlier advice. If all you are doing is comparing program arguments, then please use strcmp from the cstring library to do that. Otherwise, you really do have to create a string array to do other things, and it will NOT be called switches.

Quote:

Originally Posted by whiteflags

I'm actually losing track of what you mean.

From what I can see, switches is created as a parameter to main; its type being

char *switches[]

C string arrays and std::string arrays are not the same.

I stand by my earlier advice. If all you are doing is comparing program arguments, then please use strcmp from the cstring library to do that. Otherwise, you really do have to create a string array to do other things, and it will NOT be called switches.

That would be a good idea, however the argument is of type CHAR and strings are of type STRING and are not compatible to be compared to one another.

Looking at it like the compiler, string literals are not std::strings, they are an array type char[whatever_size], a char array. A C-string is defined as a sequence of characters followed by an immediate terminating zero. Even if you never see the zero, you can store a string literal in a char array, so they are in all important ways equivalent.

Quote:

Originally Posted by whiteflags

I'm actually losing track of what you mean.

From what I can see, switches is created as a parameter to main; its type being

char *switches[]

C string arrays and std::string arrays are not the same.

I stand by my earlier advice. If all you are doing is comparing program arguments, then please use strcmp from the cstring library to do that. Otherwise, you really do have to create a string array to do other things, and it will NOT be called switches.

Introducing strcmp to newbies? No, thank you. Let them forget C-style string and C-style comparison every existed.
I stand by my earlier advice to build C++ strings from them.
That's my opinion anyway. No need to teach them about C-style comparison. They're probably not going to need it in any near future.

Quote:

Originally Posted by camelCase

That would be a good idea, however the argument is of type CHAR and strings are of type STRING and are not compatible to be compared to one another.

Yes, they are. You can compare a C-style string to a std::string.

Maybe if argv and string literals were all std::string things it would be possible to completely forget what a C-string is.

If only we were that lucky. Not going to happen in any near future, I believe.