How to Safely Convert Between stringstream, string, and char* in C ?

Navigating stringstream, string, and char* Conversions

When working with strings in C , programmers often encounter confusion when converting between stringstream, string, and char*. This article delves into the intricacies of these conversions, unravelling misconceptions and providing practical solutions.

Understanding the Lifetime of stringstream.str().c_str()

The crux of the issue lies in understanding the lifetime of the string returned by stringstream.str().c_str(). This temporary string object is destroyed at the end of the expression, rendering any pointers obtained from it (like const char* cstr2) invalid.

Resolving the Confusion

To resolve this issue, avoid assigning stringstream.str().c_str() directly to a const char*. Instead, create a copy of the temporary string in another string object and then obtain the C string from that:

const std::string tmp = stringstream.str();
const char* cstr = tmp.c_str();

Alternatively, confine the temporary string's lifetime by using it within the expression:

use_c_str( stringstream.str().c_str() );

For efficiency and clarity, bind the temporary to a const reference:

{
  const std::string& tmp = stringstream.str();   
  const char* cstr = tmp.c_str();
}

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