During compilation, the compiler often generates several temporary files, which it then deletes to clean up. Common ones are:

1. C compilers first run the code through a preprocessor, and often use a temporary file to store the result.
2. Almost all modern compilers reduce C to an intermediate language that can be better optimized. This is often stored in a temporary file.
3. Old versions of gcc (possibly new versions, as well) would generate assembly, which was then assembled using gas (the GNU assembler). This step was done using a temporary file (with a .S extension).

The result of the compile phase then produces either one or two files:

1. An object file (.o for most Unices, .obj for Windows) that contains compiled but unlinked code. This code cannot be executed; it has external dependencies (the system library, and possibly other libraries) that must be satisfied by a linking phase.
2. If the user requests debugging information (-g under gcc), then, depending on the architecture and other compilation flags, the compiler may generate a file (or directory) that contains symbolic information used in debugging. The compiler in Mac OS X produces .dSYM directories that contain the debugging information. Under Linux, this is often embedded in the object (.o) file.

Finally, Mac, Unix, and Windows have a linking phase, which takes the object files (.o and .obj) and any required libraries (.a, and .so under Linux; .a, .dylib, or a framework under Mac OS X; .lib or .dll under Windows), and produces an executable. This is the phase that generates the executable (.exe under Windows) file.

To sum it up, when compiling an executable:

• The C compiler often creates (and then deletes) a number of temporary files.
• The C compiler generates one or more object files.
• The linker generates an executable, and may also create (and delete) temporary files.
• Some C compilers (e.g., gcc) also operate as front-end drivers for both the compiler and the linker. In this case, the compiler may delete any unneeded temporary files, such as the object files generated by the compilation phase.