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Sep 18th, 2006

Regarding Function Returning a Value.

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I have a doubt on function returning a value. Consider the following program snippet.

C Syntax (Toggle Plain Text)
 
 
 int add(int a,int b) {
   int c=a+b;
   return;
   }
 
 int main()  {
   int a=10,b=20;
   printf("%d %d %d",a,b,add(a,b));
   return(0);
   }
 
 
 int add(int a,int b) {
   int c=a+b;
   return;
   }
 
 int main()  {
   int a=10,b=20;
   printf("%d %d %d",a,b,add(a,b));
   return(0);
   }

The above program gives the output as
10 20 30

But the function is not returning any value. According to the K&R C, Section 4.1,

".......there need be no expression after return; in that case, no value is returned to the caller."

I will be grateful if anyone explains the logic behind this cryptic.

Thanks in advance.

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Iqbal_h_a

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Sep 18th, 2006

Re: Regarding Function Returning a Value.

Your code probably shouldn't compile. add(int, int) is specified to return an int, but doesn't, which should raise a compile time error.

Last edited by Infarction; Sep 18th, 2006 at 4:40 am.

Infarction

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Posting Virtuoso

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Sep 18th, 2006

Re: Regarding Function Returning a Value.

Compile your code in strict mode. I guess it should be error. Anyways return value in C on x86 is generally eax, where the result of the last calculation often happens to be placed. Maybe that's why you are seeing this result.

Grunt

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Sep 18th, 2006

Re: Regarding Function Returning a Value.

Click to Expand / Collapse Quote originally posted by Infarction ...

Your code probably shouldn't compile. add(int, int) is specified to return an int, but doesn't, which should raise a compile time error.

You are right. When I compiled in strict mode, it thrown a compilation error. But in normal mode it doesn't and it will act exactly as Grunt's explanation.
Anyway, thank you very much for your quick reply.

Iqbal_h_a

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Sep 18th, 2006

Re: Regarding Function Returning a Value.

Click to Expand / Collapse Quote originally posted by Grunt ...

Compile your code in strict mode. I guess it should be error. Anyways return value in C on x86 is generally eax, where the result of the last calculation often happens to be placed. Maybe that's why you are seeing this result.

Cool explanation and I am cleared with all my doubts and even it has thrown an error when I compiled in strict mode as you expected.
Much appreciated reply

Iqbal_h_a

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