multiple source files with main functions

You seem to be on the right trail.

To reach your goal you could go the following way:

1. rename the several main()s as by your example code to sample1_main(), sample2_main() ... (this avoids the multiple definition of error btw)
2. leave the main() from your post as is
3. modify your makefile in such a way, that depending on which sample you want to run, the executable built is called sample1, sample2, ... (for gcc the option -o specifies the name of the executable)
4. call the executable by its name, that is sample1 or sample2 or .... There is no need to pass ayn parameters.

That's it! :-)

The reason for this behaviuor is that argv[0] is the name of the executable itself.

It sounds like you want to be able to select the "main" function that executes at runtime, rather than compile-time. One way to do this is to define them as separate "entry point" functions and then have a means to select the one that runs in your main function based on the command line arguments.

So you would define main.c, sample1.c, sample2.c, etc. and in main.c you would have something like this:

int main(int argc, char **argv) {
  char *methodToExecute;

  if (argc < 2) {
    printf("usage: main.exe <sample_name>\n");
    exit(-1);
  }

  methodToExecute = argv[1]; /* argv[0] is 'main.exe' */

  if (strcmp(methodToExecute, "sample1") == 0) {
    return sample1();
  }
  else if (strcmp(methodToExecute, "sample2") == 0) {
    return sample2();
  }

  /* etc. */
  else {
    printf("method not found: %s\n", methodToExecute);
    exit(-1);
  }
}

You can use macro for main functions in other files. When compiled as library, define it as sample1_main (using gcc -D option) otherwise as main. Try something like,

sm1.c:

#include <stdio.h>

#ifndef S1_MAIN
 #define S1_MAIN main
#endif

int S1_MAIN( int argc, char ** argv)
{

    printf( "This is (sample1_main)\n" );
    return 0;
}

sm2.c:

#include <stdio.h>

#ifndef S2_MAIN
 #define S2_MAIN main
#endif

int S2_MAIN( int argc, char ** argv)
{

    printf( "This is (sample2_main)\n" );
    return 0;
}

main.c:

#include <stdio.h>
#include <string.h>

int sample1_main(int , char ** );
int sample2_main(int , char ** );

int main(int argc, char ** argv)
{
    if (argc > 1)
    {
            if (strstr(argv[1], "sample1")) return sample1_main(argc, argv);
            else if (strstr(argv[1], "sample2")) return sample2_main(argc, argv);
    }
    printf("Not sure what I should run.\n");
    return 0;
}

Compilation: (as single binary)

gcc -Wall -DS1_MAIN="sample1_main" -DS2_MAIN="sample2_main" main.c sm1.c sm2.c -o main

./main
Not sure what I should run.
./main sample1
This is (sample1_main)
./main sample2
This is (sample2_main)

Compilation: (as separate binaries)

gcc -Wall sm2.c -o sm2
gcc -Wall sm1.c -o sm1
./sm1
This is (sample1_main)
./sm2
This is (sample2_main)

Note: I have fixed main file to check the command line arguments.