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One or more multiply defined symbols found

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11 марта 2020

When I try to run this I get this error:

Terrain.obj : error LNK2005: "int __cdecl DebugMessage(char const *)" (?DebugMessage@@YAHPBD@Z) already defined in Loodus.obj

Renderer.obj : error LNK2005: "int __cdecl DebugMessage(char const *)" (?DebugMessage@@YAHPBD@Z) already defined in Loodus.obj

test.obj : error LNK2005: "int __cdecl DebugMessage(char const *)" (?DebugMessage@@YAHPBD@Z) already defined in Loodus.obj

C:UsersTiagoDesktopLoodus EngineDebugLoodus Engine.exe : fatal error LNK1169: one or more multiply defined symbols found

But why does this happen? I have #ifndef #define and #endif in the header so multiple definitions shouldn’t happen

9 Answers 9

Put the definition (body) in a cpp file and leave only the declaration in a h file. Include guards operate only within one translation unit (aka source file), not across all your program.

The One Definition Rule of the C++ standard states that there shall appear exactly one definition of each non-inline function that is used in the program. So, another alternative would be to make your function inline.

Make the function inline or declare the function in a header file and define it in a cpp file.

As a comment by Tomalak Geret’kal suggests, it’s better to use my latter suggestions than my former and move the function’s declaration to a cpp file.

(Assuming the posted code is a header, included from multiple .cpp files)

Header guards do not protect you from link-time multiple definitions. Regardless that you have ensured the header will only appear once per Translation Unit, if you have more than one Translation Unit then that’s still multiple definitions.

Write definitions in source files, and only declarations in headers.

The only exceptions are inline functions, functions defined within a class definition (though this is not recommended!) and function templates.

This function is included into every translation unit and as a result you get multiple definitions of it – each .obj file contains its own copy. When it’s time to link them all together the linker rightfully shows the above error.

You can do a few things:

  1. Move the definition to a .cpp file and keep only the declaration in the header.
  2. Use an anonymous namespace around the function in your header file (but realize it’s a hack – you will still have multiple definitions, just no name collision).
  3. Mark it as inline (although it might not always work – only if the compiler actually chooses to inline it). That’s also a hack for the same reason as above.
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Move the definition to a .cpp file.

Declare your functions in C++ files. Since you defined your function in the header file, and that header file is included from multiple source files, it gets defined for each source file that includes it. That’s why it’s reported as being defined in multiple places.

Alternatively, you could make it inline so that the code is inserted wherever it’s used instead of being defined as a separate function each time.

It looks like you are including DebugUtil.h in more than one translation unit, then linking those objects together. However, DebugUtil.h provides a definition for the DebugMessage function, so that definition exists in all of the translation units that incorporated the header. As a result, when you link the objects, the linker rightly complains that the symbol is multiply defined.

Change DebugUtil.h so that it declares DebugMessage via a prototype, but does not provide a definition, and place the definition of DebugMessage in a .c file which you will compile and link with your other objects.

That only prevents multiple inclusions in the same source file; multiple source files #include ing it will still generate multiple definitions of DebugMessage() . In general, you should either not place functions in header files at all or make them static (and usually inline , since otherwise it doesn’t usually make sense to have multiple static definitions of the same function).

100% Certain you correctly included Guards but still getting redefinition error?

For Visual Studio: I was really frustrated because I was correctly included guards, only to find out the problem was visual studio. If you have added the file to your project, the compiler will add the file twice even if you have include guards around your implementation file and header file.

If you don’t use visual studio exclusively, and say. use code::blocks sometimes, you might want to only #include the file when you detect the absence of the visual studio environment.

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If you are okay with including stdio.h, you can be a little less hackish about it:

Not the answer you’re looking for? Browse other questions tagged c++ or ask your own question.



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Я тренируюсь для использования ориентированного на объекты программирования в С++, но я продолжаю получать эту ошибку:

Однако мне кажется, что весь код написан правильно, и два ints упоминаются только в заголовке Global, и все объекты, похоже, правильно наследуются. Однако, как я только что сказал, я новичок в ООП, поэтому мне действительно нужно мнение: Также стоит упомянуть, что я использую allegro 5 для создания побочного шутера.

Две переменные int определены в файле заголовка. Это означает, что каждый исходный файл, включающий заголовок, будет содержать свое определение (включение заголовка чисто текстовое). Разумеется, это приводит к многочисленным ошибкам определения.

У вас есть несколько вариантов исправить это.

Сделайте переменные static ( static int W >). Они все равно будут существовать в каждом исходном файле, но их определения не будут видны за пределами исходного файла.

Поверните свои определения в объявления с помощью extern ( extern int WIDTH; ) и поместите определение в один исходный файл: int W >.

Вероятно, лучший вариант: сделайте переменные const ( const int W >). Это делает их static неявным образом, а также позволяет использовать их как константы времени компиляции, позволяя компилятору использовать их значение напрямую, а не выдавать код для чтения из переменной и т.д.

I am executing all my c/c++ programs in VC++ cmpiler.

using namespace std;

int main()
int age;
char sex;

cout > age;
cin>> sex;
if (age to correct this error by myself.But I counldn’t figure it out.Please help me.

    4 Contributors

  • forum13 Replies 1,771 Views 1 Year Discussion Span
  • commentLatest Post 12 Years Ago by Tom_Zeke
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Please use code tags instead, and watch spaces like in using namespace or else if .

Any problem with this?

Thanks for your reply.But still after took care of spaces,it displays that same error.Please help me.I am new to programming.

Also,i don’t know,how to give programs in code.I used

The same program works fine with me.
Which OS and compiler (version) are u using?

Compiler-Microsoft VC++ 2005 enterprise edition

Please help me.I couldn’t able to correct that problem.

There must be some information that you can see that you’re not telling us. How did you set up the project? Are there other files in it? Etc.?

Yes,the project has 2 more files with it.I thought in one project we can place more files.

Thanks for the reply and help me.How can i run this file when more that one file is stored in same project.

You can have more files, but as the linker seems to be telling you, you can’t have the same thing defined in more than one place. I don’t suppose you’d care to post all the relevant code?

This is the full error message

Ex2agesex.obj : error LNK2005: _main already defined in Ex1Sum.obj
Ex3currencydollar.obj : error LNK2005: _main already defined in Ex1Sum.obj
C:Documents and SettingsMohan.RBCHRIT7My DocumentsVisual Studio 2005ProjectsOwnProgramsDebugOwnPrograms.exe : fatal error LNK1169: one or more multiply defined symbols found
Build log was saved at "file://c:Documents and SettingsMohan.RBCHRIT7My DocumentsVisual Studio 2005ProjectsOwnProgramsDebugBuildLog.htm"
OwnPrograms – 3 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

How would i set some file as main to run in VC++

Well there you go. You’ve got main defined in more than one file. You can only have one main . Just like the messages are saying. You need a single entry point to your program — decide where it should be.

And again, if you want help with code, it is highly advisable that you post the code you want help with.

Dave thanks for your help and apologize for not asking my question properly.I thought that fatal error would be the problem for my program.

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