C++ Migration Guide

Templates and the Standard Library

The C++ standard library contains many templates, and many new standard header names to access those templates. The Sun C++ standard library puts declarations in the template headers, and implementation of the templates in separate files. If one of your project file names matches the name of a new template header, it is possible to pick up the wrong implementation file, and cause numerous, bizarre errors. Suppose you have your own template called vector, putting the implementation in a file called vector.cc. Depending on file locations and command-line options, it is possible for the compiler to pick up your vector.cc when it needs the one from the standard library, or vice-versa. When the export keyword and exported templates are implemented in a future compiler version, the situation will be worse.

There are two recommendations for preventing current and future problems:

Do not use any of the standard header names as names of your template files. All of the standard library is in namespace std, so you won't get direct name conflicts with your own templates or classes. You can still get indirect conflicts from using declarations or directives, so it is preferable not to duplicate template names from the standard library. The standard headers involving templates are as follows:
```
algorithm     bitset      complex      deque      exception 
fstream       functional  iomanip      ios        iosfwd  
iostream      istream     iterator     limits     list 
locale        map         memory       numeric    ostream 
queue         set         sstream      stack      stdexcept 
streambuf     string      typeinfo     utility    valarray 
vector
```

Put template implementations in the header (.h) file, instead of in a separate file, to prevent implementation file name conflicts. See C++ Users' Guide for more information.