How to Safely Return a Constant Char Pointer from a std::string?

Proper Return Method for a Constant Char Pointer from a std::string

In programming, error detection tools like Coverity flag potential issues. One such issue is the problematic return of a constant char pointer from a std::string, which can lead to undefined behavior.

Consider the following code:

const char * returnCharPtr()
{
    std::string someString;

    // Some processing!

    return someString.c_str();
}

The problem with this approach is that once the std::string someString is destroyed, the returned char pointer becomes invalid, pointing to freed memory. This issue can be addressed by returning the std::string itself rather than its c_str():

std::string returnString()
{
    std::string someString("something");
    return someString;
}

However, be cautious when accessing the char pointer from the returned std::string. For example, the following is incorrect:

const char *returnedString = returnString().c_str();

As the returned std::string is destroyed, returnedString remains dangling and attempting to access returnedString.c_str() will result in undefined behavior. Instead, store the entire std::string:

std::string returnedString = returnString();
// ... use returnedString.c_str() later ...

This approach ensures that the char pointer remains valid as long as the stored std::string exists.

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