Thread: arguments from another func

You will need to pass the content in argv[] to the func().

I suppose you can do it about 6 different ways:
1. Convert argv[2] to int inside main, and pass that to func().
2. Pass a char * to func, and pass argv[2] as that argument.
3. Pass a argc and char **argv (or char *argv[] if you prefer that notation - it's the same thing) to func().
The further ways are somehwat less obvious and/or meaningful, so i'll stop there.

--
Mats

Code:

#include <stdio.h>
#include <stdlib.h>

void testfunc (int x) {
	printf("%d\n", x);
}

int main (int argc, char *argv[]) {
	if (argc>2) testfunc(atoi(argv[2]));
}

atoi() is declared in <stdlib.h> so it would be a good idea to include that header.

Originally Posted by laserlight

atoi() is declared in <stdlib.h> so it would be a good idea to include that header.

oh yeah!

Originally Posted by quantt

But, If I was doing it, I took compilation error hereof what testfunc to take more arguments.

That's because you defined testfunc() to take two arguments, but you only passed it one argument.

Arguments to main are sent from the command line. These are typically called options or switches in documentation because they are usually not required (the program will behave in some specified, default way with no arguments) and they have some specified impact on how the program runs.

Program options follow the name of the program when you invoke it on the command line.
In your example you might type:
cprog 432
But that's not very useful. When it is useful, you know what the arguments mean.

This demonstrates it is possible to do batch processing with C programs, though. Meaning, you can write a program that will process files rather than spending a period of time with the user doing data entry. This can be handy for repetitious work that a user has to do, especially. For example, a program that plots the average rainfall per month over a period of several years might do batch processing, because it would be tedious and prone to human error otherwise.

Batch processing is not suitable for all programs, and knowing when to utilize it comes with experience. Usually though, if you have enough data to make a whole file, you can make a batch processing program. Even so, sometimes you will have to use data entry. Sometimes you will want to support both for user friendliness. A phone book program, for example, would have a user interface anyway even though you could make a file of new addresses and process those.

There is a special version of main if your program has command line arguments.

Code:

int main ( int argc, char **argv )

The argv parameter is a string array (as in argument vector), argc is it's length (the argument count). Together these things make it possible for you to process information pounded out on the command line. Each argument is received as-is, in a read only form, starting at position 1.

The specifics of this data structure are covered in the FAQ, if you are still confused about something. This post is not meant to cover the entire discussion from the FAQ.

Originally Posted by quantt

Well, therefore I ask this question. How to provide argument to main function?

You mean how to update values of some var in the main function?
or use return

Code:

int testfunc(int x)
{
   return 2*x;
}

int main(void)
{
   int x = 2;
   int y = testfunc(x);
   printf("Arg=%d, Res = %d", x,y);
   return 0;
}

Or - if you need to update more than one value - pass argument by pointer

Code:

void testfunc(int x, int* result)
{
   *result = 2*x;
   return;
}

int main(void)
{
   int x = 2;
   int y = 0;
   testfunc(x, &y);
   printf("Arg=%d, Res = %d", x,y);
   return 0;
}

Originally Posted by quantt

Tell me please, how to take printf len value in main function when len value located in testfunc function?

Return the value or use a pointer.

What is the testfunc function supposed to do? What is your whole program supposed to do?