How to fix C/C++ 'size_t' does not name a type

Problem:

When compiling your C or C++ program. you see the following error message:

src/main.cpp:4:11: error: 'size_t' does not name a type
 size_t mySize = 32;

Solution

In the file where the error occurs (in our example, that would be src/main.cpp), add the following line at or near the top. It must be added before the line where size_t is first used, and usually you would add that line after the last existing #include statements:

#include <stddef.h>

After adding that line, the error should be gone. Possibly you need to add said line to other files as well, so carefully check any compiler error messages if the error re-appears in other files.