Error when moving from OS X to linux Red-Hat - c++

Question

I had written my program using XCode. It works without any problems on the Mac. I was told that our projects would be compiled on Linux machines so I wanted to make sure it works on Linux before submitting. When I tried to compile on Linux, it gave me some reference errors:
/tmp/cckwoehj.o: In function `main':
main.cpp:(.text+0x9): undefined reference to `ReadFile()'
/tmp/cckwoehj.o: In function `leftSearch(NODE*, int)':
main.cpp:(.text+0x38b): undefined reference to `conflict(int**)'
main.cpp:(.text+0x3ca): undefined reference to `removeAllRowsWithLiteral(int**, int)'
main.cpp:(.text+0x3ec): undefined reference to `removeAllSpecifiedLiteral(int**, int)'
main.cpp:(.text+0x4ec): undefined reference to `conflict(int**)'
main.cpp:(.text+0x522): undefined reference to `unitPropagation(int**)'
main.cpp:(.text+0x538): undefined reference to `conflict(int**)'
/tmp/cckwoehj.o: In function `rightSearch(NODE*, int)':
main.cpp:(.text+0x992): undefined reference to `conflict(int**)'
main.cpp:(.text+0x9d4): undefined reference to `removeAllRowsWithLiteral(int**, int)'
main.cpp:(.text+0x9f3): undefined reference to `removeAllSpecifiedLiteral(int**, int)'
main.cpp:(.text+0xaf3): undefined reference to `conflict(int**)'
main.cpp:(.text+0xb29): undefined reference to `unitPropagation(int**)'
main.cpp:(.text+0xb3f): undefined reference to `conflict(int**)'
collect2: ld returned 1 exit status
The stuff I found online all talks about templates. I don't use templates. I also found one about a 32 and 64 bit OS problem which I do not have.
I have a function called ReadFile that is declared in a header. I call it from main and include that header file in main. I am not sure what the problem is. If OS X compiles and runs and Linux doesn't, I am assuming there is something OS X does internally that it thinks is obvious but Linux is not written that way. Is this a linker error? I think OS X would be programmed to do that internally.

Answer 1

You're declaring your functions in a header, but there's no definition, leading to undefined references when you try to turn main.cpp into an executable.
You need to compile all your source files and link them together (in the right order).
g++ -c ReadFile.cpp
#...
g++ -c main.cpp
g++ main.o ... ReadFile.o -o my_executable
Where the object files to the right rely on no unresolved symbols defined in the object files to its left on the commandline.

Answer 2

XCode is an IDE so I guess it handles the linking order for you.
To handle all this stuff automatically you'll have to also use an IDE and/or write a Makefile.
If you insist in a single command, yes, you can, as long as you include all source files in the line (e.g. g++ *.cpp), but this forces a full recompilation for every single change.