Assigning a function to a variable in C-CodePudding

What happens if you assign a function to a variable as shown below

unsigned char uchHeaderVer; 
uchHeaderVer = GetCodec(Page.Version);

BYTE CWAV::GetCodec(BYTE byVersion)
{
    RecorderInfoMap::iterator it;

    if ((it = m_mapRecInfo.find(byVersion)) != m_mapRecInfo.end()) {
        return (BYTE) ((*it).second.nCodec);
    } else {
        return 4;
    }
}

Version is of type BYTE and is stored in a typedef struct

CodePudding user response：

Every function, if not defined as returning void, must return a value, the type of returned value is declared at the beginning of function declaration.

  int some_func(){
// ^^ This is the type of returned variable.
      return 1;
  }

What happens in your case is simply assigning the returned value of GetCodec(Page.Version) to uchHeaderVer. And if the types uchHeaderVer and GetCodec(Page.Version) don't match, a conversion will happen, and if the conversion is not possible, you will get a compile time error.

CodePudding user response：

If the function returns a value and it matches (or can be casted) the variable type, then this value will be assigned to this variable, if not the code will not compile Example :

error: cannot convert ‘std::string {aka std::basic_string}’ to ‘int’ in assignment

If the function returns void also you will get an error :

error: void value not ignored as it ought to be

CodePudding user response：

What happens if you assign a function to a variable as shown below

You aren't assigning a function to a variable. You are calling a function, and assigning the result to that variable.

You haven't shown what BYTE is, but it is very likely to be a type alias for either unsigned char (or possibly char).

You can't assign a function to a variable, because functions aren't objects. You can only assign pointers to functions to variables, e.g.

BYTE (*pGetCodec)(BYTE) = &CWAV::GetCodec;
auto pGetCodec2 = &CWAV::GetCodec;
using GetCodecF = BYTE (*)(BYTE);
GetCodecF pGetCodec3 = &CWAV::GetCodec;