Why the simple code doesn't compile?

This is a discussion on Why the simple code doesn't compile? within the C++ Programming forums, part of the General Programming Boards category; Here is the code: Code: #include <stdio.h> extern end; extern edata; extern etext; int I; main(int argc, char **argv) { ...

  1. #1
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    Why the simple code doesn't compile?

    Here is the code:
    Code:
    #include <stdio.h>
    
    extern end;
    extern edata;
    extern etext;
    
    int I;
    
    main(int argc, char **argv)
    {
    
      int i;
      int *ii;
    
      printf("&etext = 0x%lx\n", &etext);
      printf("&edata = 0x%lx\n", &edata);
      printf("&end   = 0x%lx\n", &end);
    
      printf("\n");
      ii = (int *) malloc(sizeof(int));
    
      printf("main   = 0x%lx\n", main);
      printf("&I     = 0x%lx\n", &I);
      printf("&i     = 0x%lx\n", &i);
      printf("&argc  = 0x%lx\n", &argc);
      printf("&ii    = 0x%lx\n", &ii);
      printf("ii     = 0x%lx\n", ii);
    
    }
    But the compiler complains:
    Code:
    g++ -c -g main.cc -o main.o 
    main.cc:22: error: ISO C++ forbids declaration of `end' with no type
    main.cc:23: error: ISO C++ forbids declaration of `edata' with no type
    main.cc:24: error: ISO C++ forbids declaration of `etext' with no type

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    "extern" is not a data type. You need "extern int" or "extern void*" or whatever.

  3. #3
    Registered User whiteflags's Avatar
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    In fact I don't see why you need extern at all.

  4. #4
    Cat without Hat CornedBee's Avatar
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    Indeed, you'll just get linker errors that way.

    Also, are you aware that you're writing C code but posting in the C++ board?
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

  5. #5
    C++まいる!Cをこわせ! Elysia's Avatar
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    It's compiled using C++, though, so main must return int or you'll get another error.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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