Is bool a native C type

Question

I ve noticed that the Linux kernel code uses bool  but I thought that bool was a C   type  Is bool a standard C extension  e g   ISO C90  or a GCC extension

User · Answer

No  there is no bool in ISO C90   Here s a list of keywords in standard C  not C99     auto break case char const continue default do double else enum extern float for goto if int long register return short signed static struct switch typedef union unsigned void volatile while   Here s an article discussing some other differences with C as used in the kernel and the standard  http   www ibm com developerworks linux library l-gcc-hacks index html

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stdbool h was introduced in c99

User · Answer

No such thing  probably just a macro for int

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C99 added a bool type whose semantics are fundamentally different from those of just about all integer types that had existed before in C  including user-defined and compiler-extension types intended for such purposes  and which some programs may have  type-def ed to bool   For example  given bool a   0 1  b 2  c 255  d 256   the C99 bool type would set all four objects to 1   If a C89 program used typedef unsigned char bool  the objects would receive 0  1  255  and 0  respectively   If it used char  the values might be as above  or c might be -1   If it had used a compiler-extension bit or   bit type  the results would likely be 0  0  1  0  treating bit in a way equivalent to an unsigned bit-field of size 1  or an unsigned integer type with one value bit

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C99 has it in stdbool h  but in C90 it must be defined as a typedef or enum   typedef int bool   define TRUE  1  define FALSE 0  bool f   FALSE  if  f            Alternatively   typedef enum   FALSE  TRUE   boolean   boolean b   FALSE  if  b

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C99 defines bool  true and false in stdbool h

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C99 added a builtin  Bool data type  see Wikipedia for details   and if you  include  lt stdbool h gt   it provides bool as a macro to  Bool   You asked about the Linux kernel in particular   It assumes the presence of  Bool and provides a bool typedef itself in include linux types h

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Many years ago  when the earth was still cooling  we used this      typedef enum       false     1    0        true       false     bool      It has always worked for me

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Bool is a keyword in C99  it specifies a type  just like int or double      6 5 2      2   An object declared as type  Bool   is large enough to store the values 0   and 1

User · Answer

bool exists in the current C - C99  but not in C89 90   In C99 the native type is actually called  Bool  while bool is a standard library macro defined in stdbool h  which expectedly resolves to  Bool   Objects of type  Bool hold either 0 or 1  while true and false are also macros from stdbool h   Note  BTW  that this implies that C preprocessor will interpret  if true as  if 0 unless stdbool h is included  Meanwhile  C   preprocessor is required to natively recognize true as a language literal

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stdbool h defines macros true and false  but remember they are defined to be 1 and 0  That is why sizeof true  is 4

[c] Is bool a native C type?

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