Error macro names must be identifiers using ifdef 0

Question

I have the source code of an application written in C++ and I just want to comment something using:

#ifdef 0
...
#endif

And I get this error

error: macro names must be identifiers

Why is this happening?

User · Answer

This error can also occur if you are not following the marco rules

Like

#define 1K 1024 // Macro rules must be identifiers error occurs

Reason: Macro Should begin with a letter, not a number

Change to

#define ONE_KILOBYTE 1024 // This resolves

User · Answer

ifdef 0      endif     35 ifdef expect a macro rather than expression when using constant or expression   if 0      endif   or    if  defined PP CHECK     defined PP CHECK OTHER      endif   if  ifdef is used the it reports this error   ifdef  defined PP CHECK     defined PP CHECK OTHER      endif   Where  ifdef expect a macro rather than macro expresssion

User · Answer

Use the following to evaluate an expression  constant 0 evaluates to false     if 0       endif

User · Answer

The  ifdef directive is used to check if a preprocessor symbol is defined  The standard  C11 6 4 2 Identifiers  mandates that identifiers must not start with a digit   identifier      identifier-nondigit     identifier identifier-nondigit     identifier digit identifier-nondigit      nondigit     universal-character-name     other implementation-defined characters gt  nondigit  one of       a b c d e f g h i j k l m     n o p q r s t u v w x y z     A B C D E F G H I J K L M     N O P Q R S T U V W X Y Z digit  one of     0 1 2 3 4 5 6 7 8 9   The correct form for using the pre-processor to block out code is    if 0        endif   You can also use    ifdef NO CHANCE THAT THIS SYMBOL WILL EVER EXIST        endif   but you need to be confident that the symbols will not be inadvertently set by code other than your own  In other words  don t use something like NOTUSED or DONOTCOMPILE which others may also use  To be safe  the  if option should be preferred

User · Answer

The  ifdef directive is used to check if a preprocessor symbol is defined  The standard  C11 6 4 2 Identifiers  mandates that identifiers must not start with a digit   identifier      identifier-nondigit     identifier identifier-nondigit     identifier digit identifier-nondigit      nondigit     universal-character-name     other implementation-defined characters gt  nondigit  one of       a b c d e f g h i j k l m     n o p q r s t u v w x y z     A B C D E F G H I J K L M     N O P Q R S T U V W X Y Z digit  one of     0 1 2 3 4 5 6 7 8 9   The correct form for using the pre-processor to block out code is    if 0        endif   You can also use    ifdef NO CHANCE THAT THIS SYMBOL WILL EVER EXIST        endif   but you need to be confident that the symbols will not be inadvertently set by code other than your own  In other words  don t use something like NOTUSED or DONOTCOMPILE which others may also use  To be safe  the  if option should be preferred

User · Answer

The  ifdef directive is used to check if a preprocessor symbol is defined  The standard  C11 6 4 2 Identifiers  mandates that identifiers must not start with a digit   identifier      identifier-nondigit     identifier identifier-nondigit     identifier digit identifier-nondigit      nondigit     universal-character-name     other implementation-defined characters gt  nondigit  one of       a b c d e f g h i j k l m     n o p q r s t u v w x y z     A B C D E F G H I J K L M     N O P Q R S T U V W X Y Z digit  one of     0 1 2 3 4 5 6 7 8 9   The correct form for using the pre-processor to block out code is    if 0        endif   You can also use    ifdef NO CHANCE THAT THIS SYMBOL WILL EVER EXIST        endif   but you need to be confident that the symbols will not be inadvertently set by code other than your own  In other words  don t use something like NOTUSED or DONOTCOMPILE which others may also use  To be safe  the  if option should be preferred

User · Answer

Use the following to evaluate an expression  constant 0 evaluates to false     if 0       endif

User · Answer

The  ifdef directive is used to check if a preprocessor symbol is defined  The standard  C11 6 4 2 Identifiers  mandates that identifiers must not start with a digit   identifier      identifier-nondigit     identifier identifier-nondigit     identifier digit identifier-nondigit      nondigit     universal-character-name     other implementation-defined characters gt  nondigit  one of       a b c d e f g h i j k l m     n o p q r s t u v w x y z     A B C D E F G H I J K L M     N O P Q R S T U V W X Y Z digit  one of     0 1 2 3 4 5 6 7 8 9   The correct form for using the pre-processor to block out code is    if 0        endif   You can also use    ifdef NO CHANCE THAT THIS SYMBOL WILL EVER EXIST        endif   but you need to be confident that the symbols will not be inadvertently set by code other than your own  In other words  don t use something like NOTUSED or DONOTCOMPILE which others may also use  To be safe  the  if option should be preferred

User · Answer

Use the following to evaluate an expression  constant 0 evaluates to false     if 0       endif

User · Answer

This error can also occur if you are not following the marco rules

Like

#define 1K 1024 // Macro rules must be identifiers error occurs

Reason: Macro Should begin with a letter, not a number

Change to

#define ONE_KILOBYTE 1024 // This resolves

User · Answer

Note that you can also hit this error if you accidentally type    define  lt stdio h gt       instead of      include  lt stdio  gt

User · Answer

ifdef 0      endif     35 ifdef expect a macro rather than expression when using constant or expression   if 0      endif   or    if  defined PP CHECK     defined PP CHECK OTHER      endif   if  ifdef is used the it reports this error   ifdef  defined PP CHECK     defined PP CHECK OTHER      endif   Where  ifdef expect a macro rather than macro expresssion

User · Answer

Note that you can also hit this error if you accidentally type    define  lt stdio h gt       instead of      include  lt stdio  gt

User · Answer

Use the following to evaluate an expression  constant 0 evaluates to false     if 0       endif

[c++] Error: macro names must be identifiers using #ifdef 0

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