typeof operator in C

Question

Is typeof in C  really an operator  I m thinking because there is no polymorphism in C  that there is nothing to do at run-time   That is  the answer to typeof is known at compile-time    I can t think of a use of typeof that would not be known at compile time   So it appears to be more of a compile-time directive  than an operator     Does typeof use any  processor  run-time  in GCC

User · Accepted Answer

Since typeof is a compiler extension  there is not really a definition for it  but in the tradition of C it would be an operator  e g sizeof and  Alignof are also seen as an operators   And you are mistaken  C has dynamic types that are only determined at run time  variable modified  VM  types   size t n   strtoull argv 1   0  0   double A n  n   typeof A  B    can only be determined at run time

User · Answer

It is a C extension from the GCC compiler   see http   gcc gnu org onlinedocs gcc Typeof html

User · Answer

It s a GNU extension  In a nutshell it s a convenient way to declare an object having the same type as another  For example   int x             Plain old int variable     typeof x  y       Same type as x  Plain old int variable       It works entirely at compile-time  and it s primarily used in macros  One famous example of macro relying on typeof is container of

User · Answer

It s not exactly an operator  rather a keyword  And no  it doesn t do any runtime-magic

[c] typeof operator in C

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