The output for this code snippet is %s is a string is a string. Please explain.
#include <stdio.h>
#define scanf "%s is a string"
int main()
{
printf(scanf, scanf);
}
views:
87answers:
4
+5
A:
What exactly do you want us to explain? Subsititute the macro and get
printf("%s is a string", "%s is a string");
The rest is the expected normal everyday behavior of printf.
P.S. #define scanf ...???
AndreyT
2010-09-04 07:11:31
why is the output '%s is a string is a string' ?
Vish
2010-09-04 07:14:59
@Vish: Because that's how `printf` works and that's what `printf` does. When you read the description of `printf` in your favorite C book or doc, was there something you couldn't understand?
AndreyT
2010-09-04 07:20:23
@Vish: Think of it this way. The format string for the `printf()` call is `"%s is a string"`. There's a `"%s"` format so it takes the corresponding argument and substitutes it as a string. The first argument was the string `"%s is a string"`. Putting it all together, `"[%s is a string] is a string"` is printed (brackets added for emphasis).
Jeff M
2010-09-04 08:37:26
+2
A:
The preprocessor does a blind substitution to give:
printf("%s is a string","%s is a string");
The %s in the first argument is the format specifier for a string and is replaced with the 2nd argument. There is nothing special about the %s in the 2nd argument.
codaddict
2010-09-04 07:11:57
+1
A:
This is some rather bizarre code, but the output would be "%s is a string is a string" because scanf is expanded to "%s is a string" in both cases and then printf substitutes that in for the %s.
Dean Pucsek
2010-09-04 07:12:22
A:
printf("%s is a string","%s is a string");
I guess the confusion is what the printf will do with the second %s. To clear this, printf is not a recursive function. If you are printing a string and that string has any format-identifier it is not considered as format identifier. It is considered as plain string. So in this case the second "%s is a string" is just a plain string. %s in this string is not format-identifier.
If you had something like printf("%s %s is a string", "%s %s is a string"); Then yes you will get runtime error saying that printf is missing some argument.
Manoj R
2010-09-04 13:41:55