没有匹配的调用函数：const指向指针的指针

Question

I have the following function declaration

int vectorQuantization(const Color **input, Color **output,
                       const int rows, const int cols, const int numColors);

and when I try to call it from my main function I get the error "No matching function for call to 'VectorQuantization' ".

Color *input2quantize;
Color *outputQuantized;
...
...
vectorQuantization(&input2quantize, &outputQuantized, rows, cols, 10);

What I was trying to do is to make the input of the function constant so that it cannot be modified inside the function and I thought that declaring it as constant would make it. What am I missing here? I was thinking about using references instead pointer to pointer, but I got confused. So two questions:

1. How can I fix this error?
2. Is it better to use references instead of const pointer to pointer?

Answer 1

Say this:

typedef Color * ColorPtr;

ColorPtr input2quantize;

int vectorQuantization(ColorPtr const * input);

vectorQuantization(&input2quantize);

If you like, you can spell the function argument type out as Color * const * input , too.

Note that this protects you from having the function change the pointer , not the pointee , which cannot be protected, since you have a mutable pointer. If you wanted, you'd need a separate type:

typedef Color const * SafeColorPtr;

SafeColorPtr safeinput = input2quantize;

int foo(SafeColorPtr const * pInput);

foo(&safeinput);