deft_code deft_code - 1 year ago 87
C++ Question

Restrict passed parameter to a string literal

I have a class to wrap string literals and calculate the size at compile time.

The constructor looks like this:

template< std::size_t N >
Literal( const char (&literal)[N] );

// used like this
Literal greet( "Hello World!" );
printf( "%s, length: %d", greet.c_str(), greet.size() );

There is problem with the code however. The following code compiles and I would like to make it an error.

char broke[] = { 'a', 'b', 'c' };
Literal l( broke );

Is there a way to restrict the constructor so that it only accepts c string literals? Compile time detection is preferred, but runtime is acceptable if there is no better way.

Answer Source

There is a way to force a string literal argument: make a user defined literal operator. You can make the operator constexpr to get the size at compile time:

constexpr Literal operator "" _suffix(char const* str, size_t len);
    return Literal(chars, len);

I don't know of any compiler that implements this feature at this time.

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