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32 .\" @(#)stdarg.3 8.1 (Berkeley) 6/5/93
39 .Nd variable argument lists
43 .Fn va_start "va_list ap" last
45 .Fn va_arg "va_list ap" type
47 .Fn va_copy "va_list dest" "va_list src"
49 .Fn va_end "va_list ap"
51 A function may be called with a varying number of arguments of varying
57 and defines four macros for stepping
58 through a list of arguments whose number and types are not known to
61 The called function must declare an object of type
63 which is used by the macros
79 and must be called first.
83 is the name of the last parameter before the variable argument list,
84 i.e., the last parameter of which the calling function knows the type.
86 Because the address of this parameter is used in the
88 macro, it should not be declared as a register variable, or as a
89 function or an array type.
93 macro expands to an expression that has the type and value of the next
107 so that the next call returns the next argument.
110 is a type name specified so that the type of a pointer to an
111 object that has the specified type can be obtained simply by
116 If there is no next argument, or if
118 is not compatible with the type of the actual next argument
119 (as promoted according to the default argument promotions),
120 random errors will occur.
124 macro after that of the
126 macro returns the argument after
128 Successive invocations return the values of the remaining
133 macro copies a variable argument list, previously initialized by
139 The state is preserved such that it is equivalent to calling
141 with the same second argument used with
145 the same number of times as called with
150 macro cleans up any state associated with the variable argument list
157 must be paired with a corresponding invocation of
159 in the same function.
163 macro returns the value of the next argument.
170 macros return no value.
174 takes a string of format characters and prints out the argument
175 associated with each format character based on the type.
176 .Bd -literal -offset indent
177 void foo(char *fmt, ...)
186 case 's': /* string */
187 s = va_arg(ap, char *);
188 printf("string %s\en", s);
192 printf("int %d\en", d);
195 /* Note: char is promoted to int. */
197 printf("char %c\en", c);
206 compatible with the historic macros they replace.
207 A backward compatible version can be found in the include
225 macros were introduced in
229 macro was introduced in
236 macros do not permit programmers to
237 code a function with no fixed arguments.
238 This problem generates work mainly when converting
243 but it also creates difficulties for variadic functions that
244 wish to pass all of their arguments on to a function