Write variable parameter functions in the C language

Functions are provided with the ability to define mutable argument lists through the stdarg.h header file. The function that declares 1 variable parameter is similar to:

void f1(int n,...);

Where n represents the number of parameter lists and ellipsis represents the list of unknown parameters. An va_list type is provided in stdarg.h for storing parameters. A general usage process is similar:

void f1(int n,...)

{

va_list ap;

va_start(ap,n);  // Initializes the parameter list 

double first=va_arg(ap,double); // Take the first 1 A parameter 

int second=va_arg(ap,int);  // Take the first 2 A parameter 

...

va_end(ap); // The cleanup 

}

Look at an example of summation:

#include < stdio.h > #include < stdarg.h > 
 double sum( int  , 
);
 int main( void 
)

{

 double 
s,t;

s
 = sum( 3 , 1.1 , 2.2 , 13.3 
);

t
 = sum( 6 , 1.1 , 2.1 , 13.1 , 4.1 , 5.1 , 6.1 
);

printf(
 " return value for " 
\

 " sum(3,1.1,2.2,13.3):  %g\n " 
,s);

printf(
 " return value for " 
\

 " sum(6,1.1,2.1,13.1,4.1,5.1,6.1):  %g\n " 
,t);

 return  0 
;

}
 double sum( int  lim, 
)

{

va_list ap;

 double total = 0 
;

va_start(ap,lim);

 int 
i;

 for (i = 0 ;i < lim;i ++ 
)

total
 += va_arg(ap, double 
);

va_end(ap);

 return 
total;

}
 

The use of variable parameters in C is still a bit cumbersome, and not as easy as ruby and java. For example, variable parameters are defined and used in ruby:

def sum(*e)

e.inject{|sum,i| sum+=i}

end

sum(1,2,3,4,5)=>15