Error LNK2019 unresolved external symbol atexit

Symptoms

error LNK2019: unresolved external symbol atexit referenced in function cov_probe_v13

Cause

Your link command uses option /INTEGRITYCHECK, but does not link with the C run-time library due to the compiler option /Zl or linker option /NODEFAULTLIB.

Resolution

There are three alternatives.

Do not use /INTEGRITYCHECK when using BullseyeCoverage.
Link with the C run-time library.
- Remove compiler option /Zl
- Remove linker option /NODEFAULTLIB
- Change your entry point from WinMainCRTStartup to WinMain or from mainCRTStartup to main.

Implement atexit.

Add the code below to your application.

void (__cdecl* AtexitFunction)(void);
#if __cplusplus
extern "C"
#endif
int __cdecl atexit(void (__cdecl* func)(void))
{
	AtexitFunction = func;
	return 0;
}

Add the code below to the end of your entry point function (WinMainCRTStartup or mainCRTStartup) and before every call to ExitProcess.
```
if (AtexitFunction)
    AtexitFunction();
```

More Information

BullseyeCoverage implements the atexit using a DLL, which cannot be code signed to the requirements of the /INTEGRITYCHECK option. When /INTEGRITYCHECK is in effect, BullseyeCoverage falls back to the C run-time atexit.

Updated: 2 Dec 2024