c++ - Call of overloaded function is ambiguous

Question

What does this error message mean?

error: call of overloaded ‘setval(int)’ is ambiguous
huge.cpp:18: note: candidates are: void huge::setval(unsigned int)
huge.cpp:28: note:                 void huge::setval(const char*)

My code looks like this:

#include <iostream>
#define BYTES 8
using namespace std ;

class huge {
private:
    unsigned char data[BYTES];
public:
    void setval(unsigned int);
    void setval(const char *);  
};

void huge::setval(unsigned int t) {
    for(int i = 0; i< BYTES ; i++) {
        data[i] = t;
        t = t >> 1;
    }
}

void huge::setval(const char *s) {
    for(int i = 0; i< BYTES ; i++)
        data[i] = s[i];
}

int main() {
    huge p;
    p.setval(0);
    return 0;
}

Answer 1

The literal 0 has two meanings in C++.
On the one hand, it is an integer with the value 0.
On the other hand, it is a null-pointer constant.

As your setval function can accept either an int or a char*, the compiler can not decide which overload you meant.

The easiest solution is to just cast the 0 to the right type.
Another option is to ensure the int overload is preferred, for example by making the other one a template:

class huge
{
 private:
  unsigned char data[BYTES];
 public:
  void setval(unsigned int);
  template <class T> void setval(const T *); // not implemented
  template <> void setval(const char*);
};