With gcc set up, math.h just contains the the usual C function pow(double, double) - so all the functions work because with pow(int, int) both ints get promoted to double by compiler and all is OK.
cmath in more than a wrapper for math.h. First it includes math.h and then undefines a whole lot of stuff that math.h defined, and substitutes the c++ versions.
This includes the pow function declaration.
As the c++ overloaded functions (same as any other c++ compiler), you will get the ambiguity problem - when using pow(int, int).
P.S. - The ambiguity occurs with pow(int, int) because integers can be promoted to floats or doubles, which means that pow(int, int) can fit the so overloaded c++ pow function - so the compiler gets confused.
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