C-language function variable parameter list

Original: C-language function variable parameter list

In a function prototype, the parameters that the function expects to accept are listed, but the prototype can only display a fixed number of arguments. Is it possible for a function to accept a different number of arguments at different times? The answer is yes, but there are some limitations.
Consider a function that calculates the average of a series of values. If these values are stored in an array, the task is too simple, so in order to make the problem more interesting, we assume that they are not stored in the array. Let's take a look at a poorly-calculated and less stable solution:

1 //calculates the average of a specified number of values (bad scheme)
2 floatAverageintN_value,intV1,intV2,intV3,intV4,intV5)
3{
4    floatSUM=V1;
5    if(n_values>=2)
6Sum+=v2;
7    if(n_values>=3)
8Sum+=v3;
9    if(n_values>=4)
TenSUM+=V4;
 One    if(n_values>=5)
 ASUM+=V5;
 -    returnSum/n_values;
 -}

There are a few problems with this function: first, it does not test the number of arguments, and it cannot detect this situation where there are too many parameters. But this problem is easy to solve, simply add the test. Second, a function cannot handle more than 5 values. To solve this problem, you only have to add some similar code to the already bloated code. There is also a more serious problem: the correspondence between the real parameter and the formal parameter is not necessarily accurate.

STDARG macro
mutable parameter lists are implemented by macros that define the Stdarg.h header file, which is part of the standard library. This header file declares a type va_list and
Three macro--va_start, Va_arg, Va_end. We can declare a variable of type va_list, which is used in conjunction with these macros, to access the value of the parameter.
The following program uses three macros to correctly complete a task that calculates the average of a specified number of values.

1 //average of a specified number of values
2#include <stdarg.h>
3 float(intValues,...)
4{
5Va_list Var_arg;
6    intCount
7    floatsum=0;
8    
9Var_start (var_arg,n_values);//preparing to access mutable parameters
Ten      for(count=0; count<n_values;count+=1)//add a value from a mutable parameter table
 One{
 ASum+=var_varg (Var_arg,int);
 -}
 -Var_end (VAR_ARG);//complete processing of mutable parameters
 the     returnSum/n_values;
 -}

C-language function variable parameter list