How Can I Safely Return a Character Pointer from a C std::string?

Returning a Non-Dangling Char Pointer from std::string.c_str()

In C , returning a constant char pointer from std::string::c_str() carries potential pitfalls due to the dangling pointer issue. Understanding this issue is crucial to ensure correct and reliable programming.

Consider the code snippet:

const char *returnCharPtr()
{
    std::string someString;
    // Some processing
    return someString.c_str();
}

As Coverity reports, returning someString.c_str() presents a problem: someString's lifetime ends when the function exits, leaving the returned char pointer dangling, potentially causing undefined behavior.

To resolve this issue, one can return an object, rather than a pointer to the object's memory. The correct code is:

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

However, when calling returnString(), it's important to avoid doing the following:

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

This would still create a dangling pointer, since returnedString references memory that is no longer valid after returnString's object is destructed. Instead, store the entire std::string object:

std::string returnedString = returnString();

By following these practices, you can ensure that your code handles std::string::c_str() correctly and avoids the dangling pointer issue, preventing undefined behavior and maintaining program integrity.

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