My extern function code is not working as it suppose to do. when I run the code I get error
ld returned 1 exit status
Code:file1.c extern int add(int a, int b) { int c; c = a+b; return c; } file1.h extern int add(int a, int b); main.c #include<stdio.h> #include"file1.h" int main() { int result; result = add (4, 5); printf("%d\n", result); return 0; }
file1.c
The above extern is incorrect and needs to be removed!Code:extern int add(int a, int b) { int c; c = a+b; return c; }
Please read a book about what "extern" means and how and where to use it.
Tim S.
"...a computer is a stupid machine with the ability to do incredibly smart things, while computer programmers are smart people with the ability to do incredibly stupid things. They are,in short, a perfect match.." Bill Bryson
> ld returned 1 exit status
You forgot to compile file.c
gcc file1.c main.c
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
What's incorrect I'm following link What is an `extern` function in C?Originally Posted by stahta01
extern int incr(int);extern int add(int a, int b) { return a+b; }
Last edited by Rahul11; 08-23-2021 at 01:36 AM.
Nop, you are not understanding that an function prototype is not an full function.
Edit: The website says it is possible; but, I think an C expert would say it may just be allowed by some C compilers.
You are able to use "extern" before an function prototype; some people consider this good style like the website you linked.
You cannot use "extern" before the full function.
Tim S.
Last edited by stahta01; 08-23-2021 at 02:24 PM.
"...a computer is a stupid machine with the ability to do incredibly smart things, while computer programmers are smart people with the ability to do incredibly stupid things. They are,in short, a perfect match.." Bill Bryson
Plus, Rahul11, you need to get hold of one of the three books I listed above, and study it thoroughly!
That's not true. It's just rarely used since it is the default. Here's a valid example from the C standard:
Code:extern int max(int a, int b) { return a > b ? a : b; }You didn't actually list any books above. Rahul11 started two topics on extern, one for variables and one for functions; you listed the books in the topic on extern for variables.
Anyway, the problem should be fixed by what Salem suggested in post #3.
Look up a C++ Reference and learn How To Ask Questions The Smart Way
main.c
file1.cCode:#include<stdio.h>#include"file1.h" int main() { int result; result = add (4, 5); printf("%d\n", result); return 0; }
file1.hCode:extern int add(int a, int b){ return a > b ? a : b; }
gcc file1.c main.cCode:extern int add(int a, int b);
When I ran code I get x=1 x=4
Those results don't come from that code.
And naming your function 'add' when it returns 'max' is utterly misleading.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
main.c
file1.cCode:#include<stdio.h> #include"file1.h" int main() { int result; result = max (4, 5); printf("%d\n", result); return 0; }
file1.hCode:extern int max(int a, int b){ return a > b ? a : b; }
gcc file1.c main.cCode:extern int max(int a, int b);
warning: implicit declaration of function 'max' [-Wimplicit-function-declaration]
result = max (4, 5);
^~~
x=1 x=4
how to remove warning in code ?
why result is wrong?
A couple of things come to mind.
1. You don't include file1.h in file1.c
2. max is such a common name that you may have tripped over some other declaration. Try naming it say 'myMax'.
Also, it works for me
Code:// file1.c extern int max(int a, int b){ return a > b ? a : b; } // file1.h extern int max(int a, int b); // main.c #include<stdio.h> #include"file1.h" int main() { int result; result = max (4, 5); printf("%d\n", result); return 0; } $ gcc file1.c main.c $ gcc -Wall file1.c main.c $ gcc -Wall -Wextra file1.c main.c $ ./a.out 5
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
I think I am having issue with complier
My setup : Mingw GCC windows
Folder Extern
file1.c file1.h main.c
gcc file1.c main.c
main.c: In function 'main':
main.c:8:12: warning: implicit declaration of function 'MyMax' [-Wimplicit-function-declaration]
result = MyMax (4, 5);
^~~~~
C:\Users\~1\AppData\Local\Temp\ccn9ySO4.o:main.c.text+0x1e): undefined reference to `MyMax'
collect2.exe: error: ld returned 1 exit status
Well yeah, you have the change the name in ALL the places.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
This command work for me
gcc -o hello file1.c main.c
I would also add warning options to your compile command:Code:gcc -o hello -Wall -Wextra -Wpedantic file1.c main.c
