Why am I getting an error converting a ‘float**’ to ‘const float**’?

Question

I have a function that receives float** as an argument, and I tried to change it to take const float**.

The compiler (g++) did

Answer 1

If you converted the parameter to const float** you could then store a const float* at the memory location where the parameter points to. But the calling function thinks that this memory location is supposed to contain a non-const float* and might later try to change this pointed-to float.

Therefore you cannot cast a float** to a const float**, it would allow you to store pointers to constants in locations where pointers to mutable values are expected.

For more details see the C++ FAQ Lite.