undefined reference to `WinMain@16' collect2.exe: error: ld returned 1 exit status

Question

I am using eclipse CDT to test the Intel instructions and below is my program:

#define cpuid(func,ax,bx,cx,dx)\
__asm__ __volatile__ ("cpuid":\
 "=a" (ax), "=b" (bx), "=c" (cx), "=d" (dx) : "a" (func));
int Check_CPU_support_AES()
 {
 unsigned int a,b,c,d;
 cpuid(1, a,b,c,d);
 return (c & 0x2000000);
 }

When I compile the above code, I get linkage error as:

Info: Internal Builder is used for build
gcc -O0 -g3 -Wall -c -fmessage-length=0 -o "src\\Intel.o" "..\\src\\Intel.c" 
gcc -o Intel.exe "src\\Intel.o" 
c:/mingw/bin/../lib/gcc/mingw32/4.7.2/../../../libmingw32.a(main.o):main.c:(.text.startup+0xa7): undefined reference to `WinMain@16'
collect2.exe: error: ld returned 1 exit status

Please help me regarding the issue.

Paleethnology

This doesn't look like the entire program. Where is WinMain? – Intelligence

He doesn't have a WinMain - that's why he gets the error he's getting. – Pathway

Answer 1

Your program isn't complete. You need to implement the OS-expected entry point. In your case, that looks like it's called WinMain.

Pathway

Yes, I figured it out. I need to implement main(). Thank You. – Paleethnology

Answer 2

Yes, Main () function is missing and the compiler is not able to find an entry point for executing the program.

One more reason is even if you have written the main function but if you didnot save the .cpp file and try to compile it will give the same error.So make sure you have successfully saved the .cpp file and then compile and run your code.

Hope this will help since I have faced similar issue and I spent around hours to figure it out , Thanks

Poikilothermic

Answer 3

1. The main() function is missing.
2. Save as this code as some new file. Again run to compile the code.
3. Check the PATH environment variable.

Corollary

I am not sure that this would be the cause. WinMain wants to be compiled in a GUI program, for console programs, there is only simple main(). – Maggoty

Somehow this worked for me, compiling file.cpp was giving me this error but when I copied the same code into another file index.cpp and compiled it. It worked just fine. My code was just the iostream header, main function and a cout statement for "hello world" – Orta

Worked for me as well, Thanks, I guess just by saving the file it resolved the issue. – Anaclinal

Answer 4

In VS Code, this can happen when you haven't saved your code. Click Ctrl + s to save the code and then run the program again.

Or to make this happen automatically, go to Settings and search for "save". Scroll down and search for "Whether to save the current file before running" and enable it.

Revamp

@JanakaEkanayake - You significantly changed this answer. It was talking about some kind of auto-save option that automatically triggers before build / run, but you changed it to only talking about manually saving with a keyboard shortcut. Unless you know that there's no such feature, that's not a good edit. (The original could use some cleanup, but not changing the key point.) – Shealy

@PeterCordes I agree with you thanks for the correction – Loft

This completely fixed my problem. I was confused seeing all these answers about things I was already doing. Apparently I just had to save the file before I could run it lol. Completely unhelpful error code as usual though. – Behm

Answer 5

you have to save the file first>> Ctrl + s

Equivocation

Multiple existing answers already say this, including one mentioning ctrl + s. Please don't post "me too" answers; upvote an existing answer that worked for you. – Shealy

Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center. – Scampi

Answer 6

If you already checked all the others reasons

I also got this message and it turned out that I accidentally placed my main() inside a namespace. So it was hidden for global access

Clabo

Answer 7

Replace main() with main(int argc,char **argv), and it works for me.

Aarhus

I'm guessing the args have to be exact so the @16 decoration (number of bytes to pop for __stdcall functions) will match what CRT is looking for. Callee-pops depends on the callee declaring its args exactly. – Shealy

Answer 8

In VS code, save the file first

Schlicher

Answer 9

When I had this error, it was because I forgot to actually add filename.

Hypercorrection

Answer 10

It happen due to following reasons:

1. If you have incorrect file name format:- In this case you can rename your filename and after that you can execute you code

2. If your code don't have main() function of have incorrect spelling of main() function:- In this case correct your spelling and re-run your code

3. Sometimes if your code is not saved:- In this case you can turn on your autosave mode or save the code before execution.

Woodnote