See what the preprocessor is doing

Question

Is there anyway to see what you code looks like after the preprocessor has done all the substitutions?

score 8 · Accepted Answer · edited Dec 10 '15 at 04:38

8

For gcc just use the -E switch

gcc -E

-E Stop after the preprocessing stage; do not run the compiler proper. The output is in the form of preprocessed source code, which is sent to the standard output.

edited Dec 10 '15 at 04:38

dbush

186,650
20
189
240

answered Nov 12 '09 at 01:14

jitter

52,771
11
107
123

For MSVS users, see this old question: http://stackoverflow.com/questions/1719234/see-what-the-preprocessor-is-doing – DarenW Jan 16 '10 at 21:02

score 7 · Answer 2 · answered Nov 12 '09 at 01:13

7

That depends on your compiler. With gcc, you would use:

gcc -E source.c

answered Nov 12 '09 at 01:13

caf

225,337
36
308
455

thanks you, for the fast and accurate responce, i should havce mention i was ussing gcc. – Frames Catherine White Nov 12 '09 at 01:15

score 7 · Answer 3 · answered Nov 12 '09 at 01:20

7

Just a note about system headers (eg <stdio.h>): they are a pain when preprocessed.

gcc -E -nostdinc file.c or cpp -nostdinc file.c will not include expansion of system headers.

answered Nov 12 '09 at 01:20

pmg

103,426
11
122
196

score 2 · Answer 4 · answered Nov 12 '09 at 01:15

2

As an alternative to gcc-E, you can run cpp on your file.

answered Nov 12 '09 at 01:15

Stephan202

57,780
13
124
131

score 1 · Answer 5 · edited Oct 19 '13 at 10:00

1

Eclipse C++ IDE (CDT) has Macro Exploration control, which can be used for:

Obtaining final macro expansion
Looking through expansion process step-by-step

This is called Macro Exploration control.

edited Oct 19 '13 at 10:00

DrYap

6,345
2
29
54

answered Nov 26 '09 at 10:57

Konstantin Tenzin

11,764
3
21
20

See what the preprocessor is doing

5 Answers5