Benefits of-e parameters on GCC

There are many GCC parameters. Here is a very important parameter-e.

If we just want to pre-process the source file,-E will be useful.

 

What can it do?

(1) Expand All predefined # define defined by the user.

For example, if you have the following code:

# Define max (A, B) (a)> (B )? (A) (B ))

...

Int c = max (A, B );

After GCC preprocessing, the pre-definition will be expanded as follows:

Int c = (a)> (B )? (A) (B ));

 

(2) load all the # include files.

If we have # include <stdio. h>, after preprocessing, the program will replace it with the content of stdio. h # include <stdio. h>,

In the final program, you will not be able to find such include, more of which are # include "/usr/include/stdio. H.

With this, you can know a) stdio. h storage path in Linux, B) file structure samples, c) size_t type definition, d) many other things you want to know

 

(3) process Conditional compilation and delete code segments that do not meet the criteria.

For example, there is a code segment:

# Ifdef m

Printf ("M ");

# Else

Printf ("Nm ");

# Endif

After preprocessing, the program will become

 

Printf ("M ");

 

 

(Because no # define m is available and other rows are left blank, the Code printf ("Nm") will be deleted)

 

How to use it?

Easy to use: gcc-e a. C.

If you want to save the result, redirect it to a file, such as gcc-e. c> B. c. c Compilation: gcc-o B. c. The running effect is the same as that of. c)