char* old = s.str(); // Freezes s s.rdbuf()->freeze(0); // Unfreeze for(int i = 0; i < 100; i++)

s << "howdy"; // Should force reallocation cout << "old = " << (void*)old << endl;

cout << "new = " << (void*)s.str(); // Freezes delete s.str(); // Release storage

} ///:~

After inserting a string to s and capturing the char* with str( ), the string is unfrozen and enough new bytes are inserted to virtually assure the memory is reallocated and most likely moved. After printing out the old and new char* values, the storage is explicitly released with delete because the second call to str( ) froze the string again.

To print out addresses instead of the strings they point to, you must cast the char* to a void*. The operator << for char* prints out the string it is pointing to, while the operator << for void* prints out the hex representation of the pointer.

It’s interesting to note that if you don’t insert a string to s before calling str( ), the result is zero. This means no storage is allocated until the first time you try to insert bytes to the ostrstream.

A better way

Again, remember that this section was only left in to support legacy code. You should always use string and stringstream rather than character arrays and strstream. The former is much safer and easier to use and will help ensure your projects get finished faster.

Output stream formatting

The whole goal of this effort, and all these different types of iostreams, is to allow you to easily move and translate bytes from one place to another. It certainly wouldn’t be very useful if you couldn’t do all the formatting with the printf( ) family of functions. In this section, you’ll learn all the output formatting functions that are available for iostreams, so you can get your bytes the way you want them.

The formatting functions in iostreams can be somewhat confusing at first because there’s often more than one way to control the formatting: through both member functions and manipulators. To further confuse things, there is a generic member function to set state flags to control formatting, such as leftor right-justification, whether to use uppercase letters for hex notation, whether to always use a decimal point for floating-point values, and so on. On the other hand, there are specific member functions to set and read values for the fill character, the field width, and the precision.

Chapter 14: Templates & Container Classes

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