Undefined symbols for architecture x86_64 error when compiling

Question

Very simply, I am getting this error:

Undefined symbols for architecture x86_64:
  "Tetris::rotate(int (*) [2], int)", referenced from:
      Tetris::add_piece(char, int, int) in tetris-8a8072.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

here is my rotate function:

int** rotate(int oldpiece[][2],int rot){
    int **newpiece= new int*[4];
    for (unsigned int i=0; i<4; ++i){
        newpiece[i] = new int[2];
    }
    for (unsigned int i=0; i<4; ++i){
        for (unsigned int j=0; j<2; ++j){
            newpiece[i][j]=oldpiece[i][j];
        }
    }
    return newpiece;
}

old piece is an 4x2 array of ints.

As of now all this function should do is copy oldpiece into newpiece and then return newpiece; . I have no idea what this error means.

Answer 1

Do you have an external library? if so, you must link it. Also, try compiling the program under release option instead of debug option.