Related phrases include usage and collocation (include)

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iostream and iostream.h

#include // This is the standard header file after standardization in 1998 #include // This is the header file before standardization. The essential difference is that iostream puts the components of the standard C++ library inIn a namespace named std.On the other hand, iostream.h puts these standard components in the global space, and the old C standard library has also been transformed after standardization.To use the former, you need to add a statement in the code: using namespace std; ie: #include == #include + using namespace std;

#include, #include and #include “xxx.h”

• #include: The header files that come with the system are enclosed in angle brackets, so that the compiler will search in the system file directory.
• #include "xxx.h": User-defined files are enclosed in double quotation marks. The compiler will first look in the user directory, and then in the C++ installation directory (for example, in VC, you can specify and modify the library file search path), in Unix and Linux, it can be set by environment variables), and finally in system files.

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