va_start
From cppreference.com
| Defined in header <cstdarg>
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| void va_start( std::va_list ap, parm_n ); |
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The va_start macro enables access to the variable arguments following the named argument parm_n.
va_start should be invoked with an instance to a valid va_list object ap before any calls to va_arg.
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If the parm_n is a pack expansion or an entity resulting from a lambda capture, the program is ill-formed, no diagnostic required. |
(since C++11) |
If parm_n is of reference type, or of a type not compatible with the type that results from default argument promotions, the behavior is undefined.
Parameters
| ap | - | an object of the va_list type |
| parm_n | - | the named parameter preceding the first variable parameter |
Expanded value
(none)
Notes
va_start is required to support parm_n with overloaded operator&.
Example
Run this code
Output:
150
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| CWG 273 | C++98 | it was unclear whether va_start is required tosupport parm_ns with overloaded operator&
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required |
| LWG 2099 | C++98 | the behavior was undefined if parm_n is declared with a function, array, or reference type |
the behavior is undefined if parm_n is of reference type |
See also
| accesses the next variadic function argument (function macro) | |
| ends traversal of the variadic function arguments (function macro) | |
| C documentation for va_start
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