Main function does not return any values when calling other function.

Please help. I learning about function with return pointer value.

The function is supposed to return value from the file in my main, but I am getting empty value.

I am trying to get better with pointer. Right now just teaching myself. Please help.

right now the only way for this code to show value is when in put the putchar(*ps) inside my readfile function. I would like to readfile to return value and print in the main function.

Thanks again everyone..for reading.and helping out.

Code:

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#include <stdio.h>


char *readfile(char filename[]);


int main(int argc, char *argv[]  ) {
  char output[400];
  char *pout;
  pout = output;
 
  pout = readfile(argv[1]);
  printf("%c\n", *pout++);
}

//this is the function that takes file name.... and return pointers.
char *readfile(char filename[] ) {
  char c;
  char string[400];
  char *ps;
  ps = string;
  FILE *myfile;
  int x;


  myfile = fopen(filename, "r");
  while ((c=fgetc(myfile)) != EOF){
      *ps = c;
      x++;


  }
 return ps;


}

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ps points to the first character of string, which is a local array and thus no longer exists once control is returned from readfile to the main function. Since you seem to want to store the output in the variable named output, pass output (which will be converted to a pointer to the first character thereof) to readfile as another argument, and use that in place of ps.

Thanks Laserlight! Your quick feedback is really helpful. Now, I need to get better on passing local variable to pointer within function.

Local variables are allocated on the stack and these are "popped" when return is issued. You could allocate your string on the heap (using malloc) and that would still exist when exiting and give you the result you are expecting.

Quote:

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Originally Posted by Syscal

Local variables are allocated on the stack and these are "popped" when return is issued. You could allocate your string on the heap (using malloc) and that would still exist when exiting and give you the result you are expecting.

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If you use malloc() in readfile(), don't forget you should do a free() in main() when done with the buffer.

You could declare string in readfile() to be static, (static char string[400]; ), which will effectively make string a global variable, but with a local scope (the name for string is local to readfile(), but it's otherwise a "permanent" variable, and you could safely return a pointer to it).

laserlight's suggestion of passing "output" to readfile() as a parameter is probably the best way to do this.