how to run my own C program that prints to std out? - c

Question

I only used C 2-3 times. Following hello world tutorial did not help. the function should just print to std out console.
#include <stdio.h>
void my_putstr(char* param_1) {
char *t ;
for (t = param_1; *t != '\0'; t++) {
printf("%s", t);
}
}
int main(){
my_putstr("abc");
return 0;
}
How to run this program? I do have main to call & test my putstr function.
I do this:
gcc file.c -o file
gcc file
But it still gives me the error of "main":
(.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status
I do have the main function. What's wrong?

Answer 1

gcc file.c -o file
gcc file
That second line will try to compile the executable file that you created with the first line and, since it's not C source(a), that won't end too well :-)
You need to run the file with something like:
./file
And, just as an aside, you should strive to make your programs more readable, such as with:
#include <stdio.h>
// my_putstr:
// Output the given string multiple times, each time starting
// at the next character. So, for "1234", it would output
// "1234 234 34 4" (without the spaces).
void my_putstr(char *str) {
// Start at position 0, 1, m2, etc until no more string left.
for (char *ptr = str; *ptr != '\0'; ptr++) {
printf("%s", ptr);
}
}
int main(void) {
my_putstr("abc");
return 0;
}
Changes made:
Comments are quite handy if you ever come back to the code after some time;
You should try to avoid simple variable names, use names that make the intent clear (about the only exception are simple i, j, k loop variables;
The two canonical forms of main are int main(int argc, char **argv) (though the "or equivalent" phrase in the standard also allows for int main(int argc, char *argv[])) or int main(void), you should try to stick with them.
By the way, the description in the comments above is an accurate representation of the way the code works. If, instead, you just want to output a string (i.e., not the 1234 234 34 4 behaviour), you're probably better off with something like:
void my_putstr(char *str) {
// Output each character, one at a time.
for (char *ptr = str; *ptr != '\0'; ptr++)
putchar(*ptr);
// Output newline (if desired).
putchar('\n');
}
(a) The gcc program is quite capable of taking other input file types (like object files, assembler files, and so on) but I'm not sure finished executables are one of those types.