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Mac Forum / Programming / Mac Programming / June 2006Incompatible declaration warning - huh?
I'm using i686-apple-darwin8-gcc-4.0.1 to compile the following code: #include <unistd.h> #include <stdio.h> int main() { if((write(1, "Here is some data\n", 18)) != 18) write(2, "A write error has occured on file descriptor 1\n", 46); exit(0); } Compiling with: gcc -o simple_write simple_write.c Getting: simple_write.c: In function 'main': simple_write.c:10: warning: incompatible implicit declaration of built-in function 'exit' -Cheers > I'm using i686-apple-darwin8-gcc-4.0.1 to compile the following code: > [quoted text clipped - 20 lines] > > -Cheers "Implicit declaration" means, I think, that the compiler did not see an /explicit/ declaration of 'exit()' and made one up... badly. I note that you included <unistd.h>, and I presume you meant to draw in the standard UNIX facilities... like 'exit()'. I think you will do better if you include <stdlib.h>. Here is a treasure trove that you question spurred me to find: <http://www.opengroup.org/pubs/online/7908799/index.html> The gods of UNIX say: The <unistd.h> header defines miscellaneous symbolic constants and types, and declares miscellaneous functions. stdlib.h - standard library definitions  SignatureChris Henrich http://www.mathinteract.com God just doesn't fit inside a single religion. > I'm using i686-apple-darwin8-gcc-4.0.1 to compile the following code: > [quoted text clipped - 18 lines] > simple_write.c:10: warning: incompatible implicit declaration of > built-in function 'exit' #include <stdlib.h> m. Signaturematt neuburg, phd = matt@tidbits.com, http://www.tidbits.com/matt/ Tiger - http://www.takecontrolbooks.com/tiger-customizing.html AppleScript - http://www.amazon.com/gp/product/0596102119 Read TidBITS! It's free and smart. http://www.tidbits.com Thanks folks - that was it. > > I'm using i686-apple-darwin8-gcc-4.0.1 to compile the following code: > > [quoted text clipped - 28 lines] > AppleScript - http://www.amazon.com/gp/product/0596102119 > Read TidBITS! It's free and smart. http://www.tidbits.com > I'm using i686-apple-darwin8-gcc-4.0.1 to compile the following code: > [quoted text clipped - 18 lines] > simple_write.c:10: warning: incompatible implicit declaration of > built-in function 'exit' Others have already explained this error, but - what's the point of calling exit(0) on the very last line of main()? If you take that out, your program will behave in precisely the same way. sherm-- SignatureCocoa programming in Perl: http://camelbones.sourceforge.net Hire me! My resume: http://www.dot-app.org > > I'm using i686-apple-darwin8-gcc-4.0.1 to compile the following code: > > [quoted text clipped - 22 lines] > exit(0) on the very last line of main()? If you take that out, your program > will behave in precisely the same way. Right, I was going to mention that. Isn't return(n) from main() the same as exit(n)? m. Signaturematt neuburg, phd = matt@tidbits.com, http://www.tidbits.com/matt/ Tiger - http://www.takecontrolbooks.com/tiger-customizing.html AppleScript - http://www.amazon.com/gp/product/0596102119 Read TidBITS! It's free and smart. http://www.tidbits.com >> Others have already explained this error, but - what's the point of calling >> exit(0) on the very last line of main()? If you take that out, your program >> will behave in precisely the same way. > > Right, I was going to mention that. Isn't return(n) from main() the same > as exit(n)? m. Yeah, they're functionally identical when used in main(), so using exit(n) isn't exactly wrong - it's just rather unusual. Oh, and I was wrong about one thing - you do need one or the other if you're compiling with -Wall, to avoid a "control reaches the end of a non-void function" compile warning. sherm-- SignatureCocoa programming in Perl: http://camelbones.sourceforge.net Hire me! My resume: http://www.dot-app.org > Others have already explained this error, but - what's the point of calling > exit(0) on the very last line of main()? If you take that out, your program > will behave in precisely the same way. If you take it out *and* replace it with return 0;. Just taking it out means you'll return whatever was lying around on the stack. (Unless main() is special in this way, but since the compiler warns you that doesn't seem likely.) SignatureMichael Ash Rogue Amoeba Software |
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