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Diffstat (limited to 'gcc/doc/extend.texi')
| -rw-r--r-- | gcc/doc/extend.texi | 33 |
1 files changed, 32 insertions, 1 deletions
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi index 442fce6..fe22d34 100644 --- a/gcc/doc/extend.texi +++ b/gcc/doc/extend.texi @@ -31,6 +31,7 @@ extensions, accepted by GCC in C90 mode and in C++. * Thread-Local:: Per-thread variables. * OpenMP:: Multiprocessing extensions. * OpenACC:: Extensions for offloading code to accelerator devices. +* _Countof:: The number of elements of arrays. * Inline:: Defining inline functions (as fast as macros). * Volatiles:: What constitutes an access to a volatile object. * Using Assembly Language with C:: Instructions and extensions for interfacing C with assembler. @@ -7323,7 +7324,7 @@ truncate the copy without appending the terminating @code{NUL} character. Using the attribute makes it possible to suppress the warning. However, when the array is declared with the attribute the call to @code{strlen} is diagnosed because when the array doesn't contain a @code{NUL}-terminated -string the call is undefined. To copy, compare, of search non-string +string the call is undefined. To copy, compare, or search non-string character arrays use the @code{memcpy}, @code{memcmp}, @code{memchr}, and other functions that operate on arrays of bytes. In addition, calling @code{strnlen} and @code{strndup} with such arrays is safe @@ -10693,6 +10694,36 @@ library. @xref{OpenMP and OpenACC Options}, for additional options useful with @option{-fopenacc}. +@node _Countof +@section Determining the Number of Elements of Arrays +@cindex _Countof +@cindex number of elements + +The keyword @code{_Countof} determines +the number of elements of an array operand. +Its syntax is similar to @code{sizeof}. +The operand must be +a parenthesized complete array type name +or an expression of such a type. +For example: + +@smallexample +int a[n]; +_Countof (a); // returns n +_Countof (int [7][3]); // returns 7 +@end smallexample + +The result of this operator is an integer constant expression, +unless the array has a variable number of elements. +The operand is only evaluated +if the array has a variable number of elements. +For example: + +@smallexample +_Countof (int [7][n++]); // integer constant expression +_Countof (int [n++][7]); // run-time value; n++ is evaluated +@end smallexample + @node Inline @section An Inline Function is As Fast As a Macro @cindex inline functions |