Compiling error opencv

I'm working on opencv implemented codes which I downloaded already by svn. These codes such as SIFT or SURF and codes for opencv were working perfectly before, but suddenly I got this error while I want to compile any code concerns opencv

/usr/lib/gcc/i486-linux-gnu/4.4.3/../../../../lib/crt1.o: In function `_start':
(.text+0x18): undefined reference to `main'
collect2: ld returned 1 exit status

So how can I solve it please, I have red already some problems but they were not helpful with my case, such as I have to change the compilation code from g++ SIFT.cpp -o SIFT .... to g++ -o SIFT SIFT.cpp .... but it didn't work out wit开发者_如何转开发h me.

Thank you.

I know this is old, but I just had a similar problem (with OpenCV 2.4.4a (and also 2.4.1)) and this was the first thing that popped up on google.

I disabled the "precompiled headers" option in the OpenCV configuration (do it from cmake-gui, or pass -DENABLE_PRECOMPILED_HEADERS=OFF to cmake when generating), and everything works fine.

main is the starting point of execution of any C++ program. And you probably have forgot to build the source file that has main function. Since the file you built doesn't has main, linker failed to find the starting point of execution.

g++ SIFT.cpp fileThatHasMainFunctionDefinition.cpp -o SIFT

or alternatively provide the main in SIFT.cpp itself.