C++ Brain Teasers: Exercise Your Mind/

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Discussion: String Theory

Discussion: String Theory

Execute the code to understand the output and gain insights into overload resolution.

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Run the code

Now, it’s time to execute the code and observe the output.

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#include <iostream>
#include <string>
void serialize(const void*) { std::cout << "const void*"; }
void serialize(const std::string&) { std::cout << "const string&"; }
int main()
{
    serialize("hello world");
}

Why does passing a string to serialize cause the overload taking a void pointer to be called rather than the overload taking a string?

Overload resolution

When we’re calling a function with multiple overloads, the compiler uses a process called overload resolution to figure out which one is the best fit. The compiler does this by attempting to convert each function argument to the corresponding parameter type for each overload. Some conversions are better than others, and the best conversion is if the argument is already of the correct type.

All the overloads where all arguments can be successfully converted are added to a set of viable functions. Then, the compiler needs to figure out which overload to select from this set. If an overload has a better conversion for at least one argument and not a worse one for any of the other arguments, this overload is deemed to be the best viable function and is selected by overload resolution. If no overload is better than all the others, the call is ill-formed and fails to compile.

Have a look at this example:

serialize(int, int); // 1
serialize(float, int); // 2

Given these two overloads, suppose we call serialize like this:

serialize(1, 2);

Both overloads of serialize are viable. But the first overload has a better conversion for the first argument (int → int ...