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Diffstat (limited to '')
| -rw-r--r-- | doc/info/chap/language-facilities.texinfo | 102 |
1 files changed, 98 insertions, 4 deletions
diff --git a/doc/info/chap/language-facilities.texinfo b/doc/info/chap/language-facilities.texinfo index e30352e..13d3c07 100644 --- a/doc/info/chap/language-facilities.texinfo +++ b/doc/info/chap/language-facilities.texinfo @@ -9,6 +9,7 @@ * Non-returning functions:: Specifying that functions never return. * Variable alignment:: Aligment of variables and data types. * Member offsets:: Getting the offset of members of a structure. +* Variadic functions:: Support for variadic functions. @end menu @@ -134,7 +135,7 @@ least, the right to undefined them may be removed. @tpindex noreturn @tpindex _Noreturn A few, such as @code{exit}, functions never return, -and cannot fail. The @sc{ISO}@tie{}C11 added a +and cannot fail. The @sc{ISO}@tie{}C11 standard added a function qualifier that lets you specify that a functon never returns, that is, the process exits or changes process image before returning. Note @@ -174,9 +175,9 @@ a synonym for @code{__attribute__((noreturn))}. @fnindex @code{alignof} @cpindex @code{_Alignas} @fnindex @code{_Alignof} -The @sc{ISO}@tie{}C11 added a variable qualifier -and a function used to specify the aligned of -variable, and retrieve the alignment of a type, +The @sc{ISO}@tie{}C11 standard added a variable +qualifier and a function used to specify the aligned +of variable, and retrieve the alignment of a type, respectively, These are called @code{_Alignas} and @code{_Alignof}, by including the header file @file{<stdalign.h>}, the macros @code{alignas} @@ -226,3 +227,96 @@ structure has offset 0 and size 16. 0 + 16 = 16. @code{offsetof} is also known to be problematic in C++, because C++ supports redefining operators. + + +@node Variadic functions +@section Variadic functions + +@hfindex stdarg.h +@cpindex Variadic functions +@cpindex Functions, variadic +@cpindex Arguments, variadic +The @sc{ISO}@tie{}C89 standard added variadic +arguments for non-tradition function declarations. +The header file @file{<stdarg.h>} defines a +data type and the three macro functions. + +@tpindex va_list +@fnindex va_start +@fnindex va_end +@fnindex va_arg +@table @code +@item va_list +Data type that is used to traverse the non-fixed +arguments in a variadic function. + +@item void va_start(va_list @i{list}, @i{last}) +Initialises a @code{va_list}, specified by the +first argument. The second argument must be the +last fixed argument. + +@item void va_end(va_list @i{list}) +Deallocates resources that was allocated by +@code{va_start}. The specified list, must not +be used after calling this macro. + +@item @i{type} va_arg(va_list @i{list}, @i{type}) +Returns the next argument, the specified type +must have the same width the argument hade in +the call of the function. Note however, types +narrower than @code{int} are casted to @code{int}. +Therefore, if you call a function with @code{char} +or @code{short int} (or variant thereof), the +corresponding call to @code{va_arg} shall +specify @code{int} or a variant thereof (with +the same width as @code{int}.) +@end table + +@fnindex va_copy +The @sc{ISO}@tie{}C99 standard added the +macro @code{va_copy}. This macro copies a +@code{va_list}. + +@example +#inclue <stdarg.h> +void fun(int arg, ...) +@{ + va_list original; + va_list duplicate; + + va_start(original, arg); + va_copy(duplicate, original); + /* Use 'duplicate'... */ + va_end(duplicate); + /* Use 'original'... */ + va_end(original); +@} +@end example + +Some systems define @code{va_start} and @code{va_end} +with a @code{@{} in @code{va_start} and a @code{@}} +in @code{va_end}. Therefore, they are declared this +way in @command{slibc} if @code{_PORTABLE_SOURCE} +or @code{_LIBRARY_HEADER} is defined. + +@cpindex @code{...} +@code{...} is a syntactical language facility that +is built into the language. Therefore, @file{<stdarg.h>} +is not required when declaring variadic functions. +@file{<stdarg.h>} is only required when implemention +variadic functions. + +@hfindex varargs.h +@command{slibc} does not implement the legacy +header file @file{<varargs.h>}, that is an +incompatible alternative to @file{<stdarg.h>}. +@file{<varargs.h>} only supports traditional +function declarations, wheres @file{<stdarg.h>} +only supports modern function declarations. +In contrast to @file{<stdarg.h>}, @file{<varargs.h>} +supported variadic functions without fixed +arguments. + +@command{slibc} does not implement the +non-stanard macro @code{va_count}. + |