[Windows programming] # pragma once and # ifndef... # Define... # Endif comparison

Common methods to prevent header files from being included multiple times in C ++ include:

1) Use the # ifndef... # define... # endif macro

 

# Ifndef _ myheader_h __
# DEFINE _ myheader_h __

 

// Here is my class...

# Endif

 

2) use # pragma once

# Pragma once

// Here is my class...

 

We recommend that you use # pragma once for the following reasons:

1) the code is concise and easy to maintain. # Pragma once is much shorter than # ifndef... and avoids _ myheader_h _ redefinition or # endif inclusion range error.

 

2) Fast compilation. If # ifndef is used, the compiler reads the # include file and parses the code each time. The # pragma once compiler does not open files repeatedly, which greatly improves the efficiency.

The above two points are particularly outstanding in large-scale C ++ projects.

 

Note:# Pragma once is not an international standard, but a function of Microsoft C ++. However, most mainstream C ++ compilers have also implemented this function.

 

 

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