Predefined Macros

Several object-like macros are predefined; you use them without supplying their definitions. They fall into three classes: standard, common, and system-specific.

In C++, there is a fourth category, the named operators. They act like predefined macros, but you cannot undefine them.

• Standard Predefined Macros

• Common Predefined Macros

• System-specific Predefined Macros

• C++ Named Operators

Predefined macros 조회 방법

Predefined 매크로는 이름에 두 개의 underscore 가 붙습니다.

$ cpp -dM /dev/null 
$ cpp -dM /dev/null | wc -l
348

$ cpp -dM -xc++ /dev/null               # C++
$ cpp -dM -xc++ /dev/null | wc -l
390

공통으로 존재하는 매크로는 제외하고 출력 ( FULL JOIN )

$ awk 'BEGIN {
    while (getline < ARGV[1] > 0) a[$2]=$0
    while (getline < ARGV[2] > 0) b[$2]=$0
    for (i in a) if ( !b[i] ) print "C: ", a[i]
    for (i in b) if ( !a[i] ) print "C++: ", b[i]
}' <( cpp -dM /dev/null ) <( cpp -dM -xc++ /dev/null )

C:  #define __STDC_VERSION__ 201710L
C++:  #define __cpp_ref_qualifiers 200710
C++:  #define __cpp_exceptions 199711
C++:  #define __cpp_generic_lambdas 201304
C++:  #define __cpp_nsdmi 200809
C++:  #define __GNUG__ 9
. . .
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