How to use _CRT_SECURE_NO_WARNINGS

Question

I have compile error in my simple MFC window application generated from wizard with several lines of code:

error C4996: 'strncpy': This function or variable may be unsafe. Consider using strncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.

I set Configuration Properties>>C/C++>>Preporocessor>>Preprocessor Definitions>> _CRT_NONSTDC_NO_WARNINGS

But this does't helped. I have another very close project that generates only warning in this place and it has no _CRT_NONSTDC_NO_WARNINGS definition.

Only difference between projects is several different options in wizard.

Why _CRT_NONSTDC_NO_WARNINGS does not helps in first project and why second project compiles without problems without this definition?

Solution 1

Add by

Configuration Properties>>C/C++>>Preporocessor>>Preprocessor Definitions>> _CRT_SECURE_NO_WARNINGS

Solution 2

Under "Project -> Properties -> C/C++ -> Preprocessor -> Preprocessor Definitions" add _CRT_SECURE_NO_WARNINGS

Solution 3

If your are in Visual Studio 2012 or later this has an additional setting 'SDL checks' Under Property Pages -> C/C++ -> General

Additional Security Development Lifecycle (SDL) recommended checks; includes enabling additional secure code generation features and extra security-relevant warnings as errors.

It defaults to YES - For a reason, I.E you should use the secure version of the strncpy. If you change this to NO you will not get a error when using the insecure version.

SDL checks in vs2012 and later

Solution 4

For a quick fix or test, I find it handy just adding #define _CRT_SECURE_NO_WARNINGS to the top of the file before all #include

#define _CRT_SECURE_NO_WARNINGS
#include ...
int main(){
    //...
}

Solution 5

Adding _CRT_SECURE_NO_WARNINGS to Project -> Properties -> C/C++ -> Preprocessor -> Preprocessor Definitions didn't work for me, don't know why.

The following hint works: In stdafx.h file, please add

#define _CRT_SECURE_NO_DEPRECATE

before include other header files.

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Comments

[Balu]

Did you try with _CRT_SECURE_NO_WARNINGS ?

[Balu]

may be your project in Visual Studio has a "treat warnings as errors" option enabled.

[user1703401]

Read the error message

[vico]

"treat warnings as errors" is set to No (/WX-)

[vico]

yes, I could use strncpy_s, but why another project has no problems wit that?

[David C. Rankin]

These type problems are a classic example of why it is important to learn to build from the command line to familiarize yourself with what options your code need to compile before jumping to the IDE where a bulk of the time you spend troubleshooting problems is simply where is that option buried in VSCode?

[omni]

try using the /GS- flag

[jrh]

"I.E you should use the secure version of the strncpy." just FYI, the secure versions that the SDL checks are recommending seem to be not portable to other OSes, which would make them not suitable for cross platform development. It looks like you would have to disable this check for programs that target more than just windows.

[cal17_hogo]

why does #define _CRT_SECURE_NO_WARNINGS need to go above #include?

[E-rich]

Or per target: target_compile_definitions(myTarget PRIVATE _CRT_SECURE_NO_WARNINGS)

[Keith Thompson]

@cal17_hogo It depends on what's in the headers that are #included. If the headers don't depend on anything that requires _CRT_SECURE_NO_WARNINGS, then the #define can go after the #includes.

[Peter - Reinstate Monica]

@Keith The headers are what causes the compiler to emit the warnings. If you declare the function manually, there s no warning/error. So if you get the warning the define must go before the header. Here, it's _Check_return_ _CRT_INSECURE_DEPRECATE(ctime_s) in time.h, together with #ifdef _CRT_SECURE_NO_WARNINGS... earlier

[Mawg says reinstate Monica]

I don't see this dialog in Visual Studio 2019 :-(