What is a preprocessor?

Answer 1

A preprocessor is a program that proccesses a file before it's passed down to the compiler and the linker. It permits to define some variables so that a programmer can change the program just by changing one line of code. It permits to include header files to.

Answer 2

The pre-processor is as its name implies; it changes or processes the source code of the programmer in certain ways before the compiler actually sees the code to compile. For example, if I have the following:

# define VAL 5

if (abc 5)

so it has "pre-processed" the statement before the compiler.

Another common reason for using a pre-processor is to bring in lines of code to describe a feature or function that is used commonly without having to re-write the code over and over. This is the result of using the # include statement.

There are other statements, such as #pragma, #ifdef, etc.,that can cause conditionalized code to be included or not, depending on environment, etc.

The program I work on must compile on multiple platforms; some times parts of the code would only compile under Windows, some times only under certain Unix platforms. The pre-processor allows me to keep a common set of code for all platforms.

A very useful feature ...

Answer 3

It's a command for the preprocessor. This makes perfect sense if you know what a preprocessor is, but otherwise probably not a lot.

In computer science, a preprocessor is a program that reads source code and makes certain changes to it before handing the result off to a compiler. The point of the preprocessor is to make writing code simpler, by allowing people to (for example) include the contents of a different file inside the file actually being processed, or to define a 'shortcut' for some expression that may be used several times in the program, saving the coder from having to write it out in full each time.