How to use the #error

This is a discussion on How to use the #error within the C Programming forums, part of the General Programming Boards category; Hello, I'm trying to use #error such that when a function computes something I don't want it 'throws' an error. ...

  1. #1
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    How to use the #error

    Hello,
    I'm trying to use #error such that when a function computes something I don't want it 'throws' an error. I've read about this directive but didn't find how to make it work.

    Correct me:
    Code:
    #include <stdio.h>
    #error Array Out of bounds
    
    int foo(){
     #error Array out of Bounds
    }

  2. #2
    C++まいる!Cをこわせ! Elysia's Avatar
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    That doesn't work. #error is a preprocessor directive. So when the preprocessor sees it, it errors, no matter where in the text it is.
    The compiler does not even have a chance to run.

    It seems to me that what you are looking for is the C++ feature exceptions. They can be thrown to raise an error if something goes wrong runtime.
    C++ also features a compile-time assert which triggers an error during compile time if something goes wrong.
    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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    hmm..but I'm to use c and want to use #error to the extent it's permissible. For some reason however when I try:
    Code:
     			#if qNo < 1 || qNo > 4
    				#error  notFound
    			#endif /* bug with finding the hole */
    I get a compilation error. If I use #warning instead I don't.
    (I've tried, #error, #error "hello", but all with no success).

  4. #4
    Registered User slingerland3g's Avatar
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    Please read what Elysia is saying. You can only use #error during pre-processor logistics for helping in creating portable code. If you are needing to check for assertions during run time, then I would recommend that you read up on assert().

    Have you even google'd around for how to effectively use #error? There are many good links out there on this.

    Something on the use of assert()
    http://www.cprogramming.com/tips/sho...ount=30&page=0

  5. #5
    C++まいる!Cをこわせ! Elysia's Avatar
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    Note also that assert will prompt something like "assertion failed", pretty much halting the program and making recovery impossible. But that is the intended feature of assert - to help catch debug errors.
    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.

  6. #6
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    Maybe you're looking for the Boost Static Assertions?
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

    "the internet is a scary place to be thats why i dont use it much." - billet, 03/17/2010

  7. #7
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    Quote Originally Posted by cpjust View Post
    Maybe you're looking for the Boost Static Assertions?
    Not if he's using C

  8. #8
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    Quote Originally Posted by bithub View Post
    Not if he's using C
    Doh! Forgot which forum I was on.
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

    "the internet is a scary place to be thats why i dont use it much." - billet, 03/17/2010

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