passing 2d array in c 2b 2b in function

1If you are using GCC, then you are to pass the length of the array as a parameter to the function.
2
3void foo (int m, int arr[][m]) {
4    //...
5}
6However, there seems to be a bug in either the compiler or the documentation, as the above function prototype syntax only works when compiling C code, not C++ (as of gcc version 4.8.2). The only work-around I found was to use a void * parameter, and cast it int the function body:
7
8int foo_workaround (int m, void *x)
9{
10    int (*arr)[m] = static_cast<int (*)[m]>(x);
11    //...
12}
13There are other solutions if you do not want to rely on a compiler extension. If you don't mind a separate allocation for each row, you can use a vector of vectors, for example:
14
15std::vector<std::vector<int> > arr(n, std::vector<int>(m));