IntAdd在条件块中定义

#if defined(ENABLE_INTSAFE_SIGNED_FUNCTIONS)
...
#endif

如果你使用 c++ -你得到了

error C3861: 'IntAdd': identifier not found

但与 c 编译器让使用没有声明IntAdd，但因为_IntAdd（这意味着你使用x86和__cdecl）真的没有在任何obj或lib中定义，你得到链接器错误
如果您想使用IntAdd，请执行以下操作：

#define ENABLE_INTSAFE_SIGNED_FUNCTIONS
#include <intsafe.h>

也读了 insafe.h 的评论

/////////////////////////////////////////////////////////////////////////
//
// signed operations
//
// Strongly consider using unsigned numbers.
//
// Signed numbers are often used where unsigned numbers should be used.
// For example file sizes and array indices should always be unsigned.
// (File sizes should be 64bit integers; array indices should be size_t.)
// Subtracting a larger positive signed number from a smaller positive
// signed number with IntSub will succeed, producing a negative number,
// that then must not be used as an array index (but can occasionally be
// used as a pointer index.) Similarly for adding a larger magnitude
// negative number to a smaller magnitude positive number.
//
// intsafe.h does not protect you from such errors. It tells you if your
// integer operations overflowed, not if you are doing the right thing
// with your non-overflowed integers.
//
// Likewise you can overflow a buffer with a non-overflowed unsigned index.
//