c++ - argument type conversions

During the step of function overload resolution, the compiler identifies and ranks the conversion that can apply to each argument in a function call to convert to the type of the corresponding parameter in each viable function. 

 

possible minor converion in exact match 

 

 

• Lvalue-to-rvalue converion
• Array to pointer conversion
• Function to pointer conversion
• Qualification conversion

 

below the exact match, it is the pomotion, and actually the rand of the conversion (inlcuding the exact match is as follow):

 

 

1. Exact match 
2. Promotion (int -> float -> double)
3. Standard Conversion (double -> float -> int)
4. User defined conversion 

 

why the rank is so important, it is because during the overload function selection, there are rules for better ranked conversion.

 

 

• The conversion applied to the arguments are no worse than the conversion necessary to call any other viable function. 
• The conversion on some arguments are better than the conversions necesary for the ame arguments when calling the other viable functions.