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Conversion to std::string and return from function

 Many times I have come across code something like the below:

class AClass {

public:

    std::string getName();

};

std::string AClass::getName() {

    return "I am returning";

}

Here the member function converts the string constant to std::string while returning. This is in my opinion not necessary. This cast away some flexibility. I mean this way of converting to a std::string while returning to function does not make much sense. 

Reason: 

If we need in any place to get the name as const char* I need to reverse by calling string::c_str()

const char* pName = instanceOfClassA.getName().c_str();

However, keeping the return type as const char* has some benefits:

const char* AClass::getName() const {

    return "I am returning";

}

1. const char* pName =  instanceOfClassA.getName().getName(); // No Conversion will take place

2. std::string sName = instanceOfClassA.getName().getName(); // Conversion happens to std::string 

So, only based on usage conversion happens. It delays conversion until needed.

Now arguably, we can say that why not use c_str() to get something as const char*. I mean, let the function remain as below: 

std::string AClass::getName() {

    return "I am returning";

}

The usage may be like this:

const char* pName = instanceOfClassA.getName().c_str(); 

/*Other use of pName.... */

c_str() will return [internal buffer (C++ 11) of std::string as] const char*. But it's not reliable.

Why? The explanation is given in the link


In a line, to simplify it, we can't use data pointed by c_str() past the lifetime of std::string object or changed by a function. In both of those cases, the pointer will be invalidated. 

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