C++ Default Arguments - Declaration

Question

I created a function in my class. I put all my declarations in my header file and all my definitions in my .cpp .

In my header :

class FileReader{
 
public:
FileReader(const char*);                        //Constructor
std::string trim(std::string string_to_trim, const char trim_char = '=');

};

In my .cpp :

std::string FileReader::trim(std::string string_to_trim, const char trim_char = '='){

std::string _return;
for(unsigned int i = 0;i < string_to_trim.length();i++){
    if(string_to_trim[i] == trim_char)
        continue;
    else
        _return += string_to_trim[i];
}

       return _return;
}

Whenever I try to compile and run it, I get two errors.

error: default argument given for parameter 2 of 'std::string FileReader::trim(std::string, char)' [-fpermissive]

error: after previous specification in 'std::string FileReader::trim(std::string, char)' [-fpermissive]

What am I doing wrong? I just want my function to have this default argument.

Solution 1

You should not specify the default argument both in the function declaration and in the function definition. I suggest you putting it in the declaration only. For instance:

class FileReader{
public:
    FileReader(const char*);                        
    std::string trim(std::string string_to_trim, const char trim_char = '=');
    //                                                                ^^^^^
    //                                                     Here you have it
};

std::string FileReader::trim(std::string string_to_trim, const char trim_char)
//                                                                  ^^^^^^^^^
//                                              So here you shouldn't have it
{
    // ....
}

In case both the function definition and the function declaration are visible to the compiler from the point where the function call is being made, you would also have the option of specifying the default arguments in the function definition only, and that would work as well.

However, if only the declaration of the function is visible to the compiler, then you will have to specify the default argument in the function declaration only, and remove them from the function definition.

Solution 2

inside the cpp you don't need the default parameter , only in the h file

Comments

[Normal People Scare Me]

Well Thanks, worked. I removed the default argument in my definition.

[Andy Prowl]

@CGuy: That's strange. What compiler are you using? It works here.

[Normal People Scare Me]

@AndyProwl the gnu c++ compiler

[Andy Prowl]

@CGuy: See the update to my answer. If you are invoking the function from a point where only the declaration is visible, you will have to put the default argument in the declaration only.