Undefined reference error in a C program

Question

I wrote a C program pgm.c. It contains a function readfile.so. Also I wrote a header file do.h. Then I wrote this readfile function in a separate program ini.c and included do.h to this program too. When I compiled pgm.c I got the error "pgm.c:(.text+0x2e): undefined reference to readfile"

My codes are :

do.h
    extern int readfile( FILE *in );

pgm.c
    #include<stdio.h>
    #include"do.h"
    int main(int argc,char **argv)
    {
     FILE *in;
     in=fopen(argv[1],"r");
     readfile(in);
    }

ini.c
    #include <stdio.h>
    #include <stdlib.h>
    #include <limits.h>
    #include <math.h>
    #include <float.h> 
    #include"do.h"
    int c;
    int readfile( FILE *in )
    {
    while( c == '#' || c == '\n' )  
    {
      if( c == '#' ) 
       {
        while( ( c = getc(in) ) != '\n' );
       }
      if( c == '\n' ) 
       c = getc( in ); 
     }
      if( c == EOF )
      break;
      else
      {
      printf("hai");
      }
    }
    return 1;
    }

Is there any error in my programs? compiling by gcc pgm.c

no need to declare function `extern`, they're extern by default — mangusta, Mar 09 '14 at 08:43
where is the command line you use to compile & link ? add the complete line, because it looks like you don't compile and link with "ini.c" — alexbuisson, Mar 09 '14 at 08:43
possible duplicate of [What is an undefined reference/unresolved external symbol error and how do I fix it?](http://stackoverflow.com/questions/12573816/what-is-an-undefined-reference-unresolved-external-symbol-error-and-how-do-i-fix) — Luchian Grigore, Apr 09 '14 at 11:05

score 4 · Answer 1 · answered Mar 09 '14 at 08:44

4

C is case sensitive;

extern int readfile( FILE *in );

doesn't declare the same function as;

int readFile( FILE *in )

Pick a casing and use it everywhere for the same function.

answered Mar 09 '14 at 08:44

Joachim Isaksson

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i tried..change `int readfile( FILE *in );` in do.h.but again got same eroor – user39133 Mar 09 '14 at 08:51
It's implementation-defined as to whether linking is case-sensitive or not. – M.M Mar 09 '14 at 08:52
Did you read the comments below your question? Your problems are not only in the code – deviantfan Mar 09 '14 at 08:56
@user39133 Try changing `int readFile( FILE *in )` to `int readfile( FILE *in )` – Joachim Isaksson Mar 09 '14 at 14:06
@user39133 You also need to compile with `gcc pgm.c ini.c` – Joachim Isaksson Mar 09 '14 at 14:15

score 0 · Answer 2 · answered Mar 09 '14 at 08:45

0

Also you need to check the return value of fopen.

If it returns NULL then your function readfile (depending on capitalization) will crash

answered Mar 09 '14 at 08:45

Ed Heal

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Undefined reference error in a C program

2 Answers2