Preprocessor - sample

Question

1.00/5 (1 vote)

See more:

C++

#include <stdio.h>
#define SIZE 10;
#define FUDGE SIZE -2;
int main()
{
    int size;/* size to really use */
    size = FUDGE;
    printf("Size is %d\n", size);
    return (0);
}

what is the value of size in o/p for the following program?

Posted 16-Jan-13 23:19pm

mvigsnhwar

Updated 16-Jan-13 23:33pm

Jochen Arndt

v3

Add a Solution

2 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Jochen Arndt · Accepted Answer · 2013-01-16T23:40:00

Solution 1

Did you compile and run it?
And the result is not as expected?
It is as expected when you perform the preprocessor tasks yourself:

C++

size = FUDGE;
// replace FUDGE = SIZE -2;
size = SIZE -2;;
// replace SIZE = 10;
size = 10; -2;;

Did you see your mistake? #define statements need no trailing semicolon. If there is one, it is also inserted.

Posted 16-Jan-13 23:40pm

Jochen Arndt

Comments

mvigsnhwar 17-Jan-13 5:56am

yes sir i have compiled it without removing the semicolons the o/p is "Size is 10"
with removing the semicolons the o/p is "Size is 8"

Jochen Arndt 17-Jan-13 6:15am

Thank you for your feedback and accepting the answer.

I have another note which may be helpful for you and others reading this question:

Using #define statements can sometimes result in not expected behaviour. Another example is not using parenthesis when the definition is not a single literal. Consider your example '#define FUDGE SIZE -2' when using it like this:
size = 3 * FUDGE;
This will be 3 * 10 - 2 = 28 rather than the expected 3 * (10 - 2) = 24. To avoid this always use parentheses:
#define FUDGE (SIZE - 2)

mvigsnhwar 17-Jan-13 7:40am

Thank u sir :)

H.Brydon 17-Jan-13 13:45pm

Correct ... +5 for this point.

Sergey Alexandrovich Kryukov 17-Jan-13 7:33am

Right, a 5.
—SA

mvigsnhwar 17-Jan-13 8:43am

in this case semicolon permitted ah?

#include<stdio.h>
#define JOIN(s1, s2) printf("%s=%s %s=%s \n", #s1, s1, #s2, s2);
int main()
{
char *s1="Hello";
char *s2="World";
JOIN(str1, str2);
return 0;
}

mvigsnhwar 17-Jan-13 8:46am

for the above #define JOIN program when it gets replaced it is replaced as printf("%s=%s %s=%s \n", #s1, s1, #s2, s2);; in the place of printf("%s=%s %s=%s \n", #s1, s1, #s2, s2);

Jochen Arndt 17-Jan-13 9:07am

Semicolon is always permitted. If there is one at the end of the define macro definition, it is inserted. If there is also one behind the used macro, you will have two at the end. This is no problem for the compiler (the second one is treated as the end of an empty instruction which is finally removed).

In general such macros should not be used anymore. A better solution is the usage of inline functions (here for your swap example):
inline void swap(int x, int y) { int t = x; y = x; y = t; }

With C++ you can define more with the same name with other parameter types:
inline void swap(double x, double y) { double t = x; y = x; y = t; }

For constants you may use const variables rather than definitions:
const int size = 10;
const int fudge = size - 2;
The 'const' keyword specifies that the content of the variable cant be changed (e.g. using 'size = 20;' later will throw a compiler error) and the compiler will usually replace it with the literal value.

The advantages of inline functions and const variables are type checking and avoiding all the side effects of definition macros.

Richard MacCutchan · Accepted Answer · 2013-01-17T00:13:00

Solution 2

You should not put semi-colons at the end of #define statements, they may have unwanted side effects in your code.
When using expressions in #defines you should put them in parentheses, for the same reason.

Posted 17-Jan-13 0:13am

Richard MacCutchan

Comments

Sergey Alexandrovich Kryukov 17-Jan-13 7:33am

Right, a 5.
—SA