macro
<cstdarg>
type va_arg ( va_list ap, type )
Retrieve next argument
This macro expands to an expression that has the type type and the value of the next argument in the variable arguments list.
The next call to this macro will expand to the following argument in the same order as passed to the function.
Notice that va_arg cannot determine the actual type of the argument passed to the function, but uses whatever type is passed as the type macro argument as its type.
Notice also that va_arg does not determine either whether the retrieved argument is the last argument passed to the function (or even if it is an element past the end of that list). The function should be designed in such a way that the amount of parameters can be inferred in some way by the values of either the named parameters or the additional arguments already read.
Parameters
ap
Object of type
va_list with information about the additional arguments an their retrieval state. This object shall have been initialized by an initial call to
va_start before the first call to
va_arg.
type
A type name. This type name is used as the type of the expression this macro expands to (i.e., its return type).
For a type expression to be suitable for its use with va_arg it must be such that when an asterisk (*) would be appended to its right the resulting expression would be a valid pointer type to a type object.
Return Value
Returns the next additional argument as an expression of type type.
Example
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/* va_arg example */#include <stdio.h>#include <stdarg.h>int FindMax ( int amount, ...){ int i,val,greater; va_list vl; va_start(vl,amount); greater=va_arg(vl,int); for (i=1;i<amount;i++) { val=va_arg(vl,int); greater=(greater>val)?greater:val; } va_end(vl); return greater;}int main (){ int m; m= FindMax (7,702,422,631,834,892,104,772); printf ("The greatest one is: %d\n",m); return 0;}
This FindMax function takes as its first parameter the amount of additional arguments it is going to get. The first additional argument is retrieved and used as an initial reference for comparison, and then the remaining additional arguments are retrieved in a loop and compared to return the greatest one (which in this case is 892).
See also
va_startInitialize a variable argument list (macro)
va_endEnd using variable argument list (macro)
va_listType to hold information about variable arguments (type)
vsprintfPrint formatted variable argument list to string (function)
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