How below macro is working in c programming language?

Question

Code:

#include <stdio.h>
#define puts "%s C preprocessor"
int main()
{
    printf(puts, puts);
    return 0;
}

Output:

%s C preprocessor C preprocessor

See also...

Can anyone explain me the logic behind this output?

I tried to solve it,but I didn't get the proper explanation through my friends. If anyone can explain me ,it'll be very helpful.

Post code as text here instead of an external link of an image. Tell us what you have done so far to solve your problem. Macros are covered in any textbook on c. Don't shout (use all upper case). — Allan Wind, Nov 27 '22 at 09:06
What is your closest explanation you can come up with? What did you find out how the macro is replaced by preprocessor? Which part is missing then to get the output? — Gerhardh, Nov 27 '22 at 09:17
@Gerhardh , no part is missing. closest explanation would be % s is taking next argument as a string — sakshi monst, Nov 29 '22 at 08:17
Welcome to Stack Overflow! Please [edit] your post to add code and data as text ([using code formatting](https://stackoverflow.com/editing-help#code)), not images. Images: A) don't allow us to copy-&-paste the code/errors/data for testing; B) don't permit searching based on the code/error/data contents; and [many more reasons](https://meta.stackoverflow.com/a/285557). Images should only be used, in addition to text in code format, if having the image adds something significant that is not conveyed by just the text code/error/data. See [mcve] on what code is required. — Adriaan, Nov 29 '22 at 08:47

Andy A. · Accepted Answer · 2022-11-29T09:12:02.023

0

The macro let to (code after linker):

int main
{
    printf("%s C preprocessor", "%s C preprocessor");
    return 0;
}

printf works like:

The output is then

%s C preprocessor C preprocessor

edited Nov 29 '22 at 09:12

answered Nov 29 '22 at 07:44

Andy A.

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what's the reason behind this output? – sakshi monst Nov 29 '22 at 08:12
A, reason for this outpul? why is%s got printed? – sakshi monst Nov 29 '22 at 08:16
Well, at first the linker changes the code because of the macros. Then printf has 2 identical strings. The first string is taken as formatstring, the second one as a simple string. Then printf replaces the "%s" in the formatstring by the second argument. There the "%s" will not be replaced, because its not in the formatstring. – Andy A. Nov 29 '22 at 08:17
Added an image of how the substitution in printf works – Andy A. Nov 29 '22 at 08:21
if i need to go through this topic in detail about formatstring, which topic would you suggest me to study? – sakshi monst Nov 29 '22 at 08:22
The image in in the answer. I added it there. - And to get information about printf, type it in your favorite search engine. – Andy A. Nov 29 '22 at 08:26
thankyou andy, it's so much clear with the help of an image. – sakshi monst Nov 29 '22 at 08:29
"Ein Bild sagt mehr als tausend Worte" :-) ... One Look Is Worth a Thousand Words – Andy A. Nov 29 '22 at 08:31
yes, absolutely – sakshi monst Nov 29 '22 at 08:34
one more thing, in this printf is working from right to left? – sakshi monst Nov 29 '22 at 08:39
2

And now, be so kind an rewrite your question with lowercase letters. To write all uppercase classified as rude! – Andy A. Nov 29 '22 at 08:39
`printf ( FORMAT, LIST )` -> `printf ( FORMAT, x, y, z)` -> All "%" in "FORMAT" will be replaced by the elements of the list. You have to look at a tutorial!!! – Andy A. Nov 29 '22 at 08:43
i didn't know that, uppercase is considered as rude. thankyou for telling me. – sakshi monst Nov 29 '22 at 08:45

How below macro is working in c programming language?

1 Answers1