int main(int argc, char *argv[])


and some times


int main(int argc, char *argv[1])

The function main is defined with two arguments:
The first argument is an int.
The second argument is an array of pointers to char.
The function main() returns an integer value to whatever program invoked it. (Typically an operating system shell, such as bash or cmd32.exe, but programs can also be invoked from other programs --- for example: with system() function calls.)

Upon entrance to this program, the value of argc tells us how many arguments were on the command line.

For Windows and Linux systems there is always at least one command-line argument: the program name itself. Sometimes argv[0] contains the entire path to the executable; sometimes only the program name itself --- it depends on the compiler. For embedded systems, it may be that the argc-argv mechanism isn't even implemented, so argc may be zero, and argv[0] will be a "NULL" pointer.

Anyhow, back to reality:

argv[0] is treated as a C-style "string" that tells us how the program was invoked.

argv[1], argv[2], ... argv[argc-1] are treated as C-style "strings" that are the command-line arguments that were present when the program was invoked.


That's not the usual way of writing it, but in fact in a function definition, stuff inside the [brackets] in a 1-dimension array declaration is ignored, so the effect is exactly the same as the first example

You might have seen

In this case, argv is declared as a "pointer to a pointer to char". The effects on the C compiler (and, therefore, on the code) are exactly (yes, exactly) the same as the first example. It's because of how pointers are related to array index values in C (and C++) language notation.

Anyhow, you can try the following test:


With GNU gcc, I called the file "test.c" and compiled it, then ran it a few times


Lines beginning with '$' are the command lines on my system and they show what I entered.
The other lines show the program's output.

Regards,

Dave

Footnote:
The program that I gave is a valid C program and is also a valid C++ program. If you want to do things the "C++" way, then you can use "cout << " instead of printf(). (Of course the header will change to <iostream>, and you may have to give some namespace information also.)

thanks. understanding

but i run this in C++ it just says the program file name and in C it comes up with an error " main function not defined" .

Did you paste the exact program from my post into your text editor? How are you compiling the program?

Just to be sure that what I posted can work, I pasted the code from my previous post to my text editor and saved it.

This file:
I named the file "test.c" and compiled it (as a C program) with Microsoft Visual C++ version 6, Microsoft Visual C++ 2005 Express, Borland bcc32, GNU gcc.

I copied the file to "test.cpp" and compiled it (as a C++ program) with Microsoft Visual C++ version 6, Microsoft Visual C++ 2005 Express, Borland Bcc32, GNU g++

All were successful in replicating my previous results.

Here are a few runs on my Windows XP platform after compiling with the Borland compiler:


Here are the results from Microsoft Visual C++ 2005 Express:

Note the differences in how argv[0] is presented. As I mentioned, that is system-dependent. The other arguments are handled identically, as they should be according to the C (and C++) standard.

Regards,

Dave

For the C i used icc win32 and
C++ i used vs2005

How did you compile the code? How did you execute it? I executed from a command line. (Open a console window and navigate to the directory where the executable is located and enter the program name with command-line arguments as I showed.)

If the code that I posted gave a compile error, then your compiler setup is incorrect. I have no knowledge of icc win32, but all C compilers should compile it, assuming you have a valid installation.

Have you compiled any other programs with your setup (Hello, world, or whatever)?

Regards,

Dave

well i am sure it is the compilar. thanks

Since this is a C++ forum, I usually prefer to see Stroustrup's own...


...note cuddling the pointer "*" with the typename.


:davis: