I'm trying to use gcd function from #include <numeric> in Visual Studio 2019 (Community version). However, using namespace std, visual studio just says that "gcd" is undefined. Based on my research, I'm supposed to change the C version. However, in the normal settings I can't find "Configuration Properties" and right clicking on the project in the solution explorer to then select properties, just shows me an empty window (see emtpy-property-window picture).

Background info:

• Created project with C (Cmake Project) in Visual Studio 2019 Community
• Added a C file (.cpp) with main function and one class
• For Building I'm using Cmake
• Using namespace std and #inlcude <iostream> so far (with no problem)
• When using #include <numeric> and then trying to use gcd(x,y), I get the previous described error-hint
• Visual Studio tries to fix the error with adding namespace std, even though that's already added.

Any idea to solve either problem?

CodePudding user response：

The gcd function was added in C 17. You probably haven't set the appropriate standard in your project settings. At least this is the exact issue you'll get when trying to use std::filesystem::... with an older C standard with Visual Studio. (The file system library was added in C 17 too.)

In the project properties Configuration Properties > General > C Language Standard should be set to ISO C 17 Standard (/std::c 17) to make the code compile.

You can open the project properties by selecting Properties in the context menu for the target shown in the solution explorer btw; the properties shown in your screenshot just display some very basic information about the selected item.