Thread: Do I need to va_end before va_start ?

  1. 03-07-2011 #1
    Richardcavell
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    Do I need to va_end before va_start ?

    Hi, everyone. I'm using a variable number of arguments to a function using <stdarg.h>.

    My code steps through the parameters twice. Do I need to call va_end () before I call va_start the second time?

    Richard

    Code:
    int myfunction ( int i , ... )
{
    va_list va ;
    va_start ( va , i ) ;

    ...

    va_start ( va , i ) ;

    va_end ( va ) ;
}
  2. 03-07-2011 #2
    Salem
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    Yes, you do.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
  3. 03-07-2011 #3
    Mr.777
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    Better, don't ask such questions, just try those and then ask.....
  4. 03-07-2011 #4
    Salem
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    It's better to read the standard to find out what is guaranteed to work, rather than merely trying stuff to see what your current compiler will let you get away with.

    Quote Originally Posted by draft c99
    7.15.1 Variable argument list access macros

    [#1] The va_start, va_arg, and va_copy macros described in
    this subclause shall be implemented as macros, not
    functions. It is unspecified whether va_end is a macro or
    an identifier declared with external linkage. If a macro
    definition is suppressed in order to access an actual
    function, or a program defines an external identifier with
    the name va_end, the behavior is undefined. Each invocation
    of the va_start or va_copy macros shall be matched by a
    corresponding invocation of the va_end macro     in the function
    accepting a varying number of arguments.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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