Unknown type name & #39; NSString & #39;

If you see a problem today, the editing project prompts "Unknown type name 'nsstring', as shown in figure

 

The exception occurs because ZipArchive is added to the project (a third-party open-source decompression library)

 

Generally, the "Unknown type name" header file is referenced by each other. This can be ruled out because the source code is mixed with c \ c ++ and oc,

Considering the new XCode compilation file type, I tried several solutions. The following three solutions can solve the problem.

 

Solution 1:

Select All. c files and change the attribute identity and type to Objective-C Source.

Solution 2:

Select All. c files and change. c to. m.

 

Solution 3:

Change Compile Sources As to Objective-C ++

Solution 3: Because the compilation type of all files is modified, all other prompts, including c and c ++ Code, may be incorrect. However, some prompts may be incorrect. simply modify the settings as prompted.