So far have seen that function definition matches with function declaration. Sometimes it is necessary or convenient to design a function that can be called with either a different number or type of arguments. Library functions like printf and scanf

printf (“%d%f%s%c”, x, y, msg, ch);
printf (“%s %c”, str, *cptr);

work this way. This task can be achieved by making the function to accept a pointer to an array. Another way to accomplish this task is to write function that can take any number of arguments.

For performing this task, C has a header file by name stdarg.h that contains library functions to accept variable number of arguments. To use a function with variable number of arguments, the function shown in table are found very useful.

some useful functions for implementing a function for variable number of arguments

The declaring the function must have the following property:

• • Must have at least one fixed argument
• • Fixed arguments(s) listed first, must have data type
• • Use ellipses after the last fixed argument to denote start of variable arguments
• • Must design so that function can determine the number and type of the variable arguments

For example:

int max (int count, ….);

where max is the name of the function, count is fixed argument, the ellipses (. . .) indicate the variable number of arguments.

Accessing the arguments

Declare a local argument pointer of type va_list

Va_list varptr;

Use function va_start to position to first variable arg

va_start (varptr, startarg);

where varptr is the previously – defined argument pointer and startarg is the argument in the function declaration that precedes the first variable arg you went (usually the last fixed arg)

Use function va_arg, specifying data type, for each variable argument accessed

va_arg (varptr, datatype);

datatype is any valid data type, including user_defined structure, union and enumeration types.

Use function va_end when finished processing argments

va_end (varptr);

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