It also tells you the definition in Bot.o came from line 18 in the source file Bot.cpp, which is the same place in the source as the other definition. This tells you that the definition in Server.o is a multiple definition because there is also a definition in Bot.o. Now look at the next line:īot.o:/home/ubuntu/NetBeansProjects/SemestralniPraceChat/./Bot.cpp:18: first defined here This message says that the object file Server.o contains a multiple definition of the function Bot::getRandomMessage() function, and that the multiple definition comes from line 18 in the source file Bot.cpp. home/ubuntu/NetBeansProjects/SemestralniPraceChat/./Bot.cpp:18: multiple definition of `Bot::getRandomMessage()' Start with the first lines: Server.o: In function `Bot::getRandomMessage()': So when the compiler starts on the file "main.cpp" that the preprocessor has inserted the extra lines into (the file after the preprocessor has finished with it is commonly called a "translation unit"), it will see that declaration before you try to use the function, and everyone is happy.Look at what the error messages are telling you.
#Codeblocks compiler error multiple function definitions code
So your "main.cpp" file would have, near the top, #include "action.h", the pre-procesor would open the file "action.h", and copy into "main.cpp" the declaration you wrote in "action.h", and now "main.cpp" has an extra line of code in it the declaration of the function, near the top, before you try to use the function. You could then use the #include pre-processor directive to have all those declarations put into your code wherever you like, and the pre-processor will type the contents of the file included file into that spot, just as if you had typed it yourself. So, you could create a file named "action.h", and put in it the declaration of every function that is defined in "action.cpp" This is simply a plain text file containing useful things such as function declarations. Alternatively, you could create what we commonly refer to as a header file. You can do this by just typing that declaration in. So you need to put this in your code, somewhere before you try to call the function. The declaration is the bare minimum the compiler needs to know the name, the return type, the input parameters.įor the function actioncmd, the declaration is as follows: The second way is to have a declaration of the function in that source file, somewhere before you try to use it. This is what you were trying before, and because you were doing it in more than one *.cpp file, you hit the problem that you had the exact same function defined in more than one place. The first way is to have the complete definition of the function in that source file, somewhere before you try to use it. There are two ways to ensure the compiler knows what it needs to know about the function in order to use it. Each time the compiler starts on a new source file, anything it learned about a previous source file no longer matters This must be done separately for every source file being compiled. Specifically, it must know the function's name, its return type, and its input parameters. To use a function in C++, when the compiler gets to the point at which you try to use it, the compiler must know about the function already. # include project implementation makefile GlutCreateWindow("OpenGL") // creating the windowĬhar* appendCharToCharArray(char* array, char a) GlutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA) // enabling double buffering and RGBA Static void key(unsigned char key, int x, int y)Ĭmdval=appendCharToCharArray(cmdval,key) Omit this line if you don't want constant redraw
GlutSwapBuffers() // swapping image buffer for double buffering
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