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PROGRAM ARGUMENTSPROGRAM ARGUMENTS
Command line argumentsArguments that we pass on to main() at
the
command prompt
Variable number of argumentsHow to write functions that accepts
the variable
number of arguments
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Command Line ArgumentsCommand Line Arguments
Argc and argv - arguments handled by
main().
Argv-char array of pointers to strings Argc-number of strings to
which argv
points,it is an integer
General form of main() with command linearguments.
main ( int argc, char *argv[ ] )
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Command line argumentsCommand line arguments--ExampleExample
Main(int argc,char *argv[])
{
If(argc!=2)
Printf(invalid input format);Else
Printf(Length of the string is:%d,strlen(argv[1]));
}
>./a.out command /*argv[0]=./a.out argv[1]=command*/
Length of the string is:7
>./a.out
Invalid input format
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Variable number of argumentsVariable number of arguments
Some functions in the standard library acceptsvariable number of
arguments.
Printf() and scanf() are the examples.
Let us discuss variable number of argumentswith an example.
double average(double v1,double v2 )Function is used to compute
the average
Denotes that the function has a variable number ofarguments
Above statement demonstrates the prototype of function
withvariable number of arguments.
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Variable number of argumentsVariable number of arguments
Must have atleast one fixed argument,inour example it is 2.
Now, how to reference the argumentswhen writing the
function.
Stdarg.h header provides three macros toaccess the
arguments.
Va_startVa_arg
Va_end
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Va_start() macroVa_start() macro
General form:
void va_start(va_list parg, last_fixed_arg);
Variable argument start accepts twoarguments.Pointer parg of
type va_list
Name of the last fixed parameter
Va_list is defined in stdarg.h and it is usedto store
information required by theroutines
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Va_start() macroVa_start() macro
Va_start macro for an average function
can be like this.
double average(double v1, double v2, ...){
va_list parg; /* Pointer for variable argument list */
/* More code to go here... */
va_start( parg, v2);
/* More code to go her. . . */
}
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ExampleExample
double average( double v1, double v2,...)
{
va_list parg; /* Pointer for variable argument list */
double sum = v1+v2; /* Accumulate sum of the arguments */
double value = 0; /* Argument value */
int count = 2; /* Count of number of arguments */
va_start(parg,v2); /* Initialize argument pointer */
while((value = va_arg(parg, double)) != 0.0)
{
sum += value;
count++;
}
va_end(parg); /* End variable argument process */
return sum/count;
}
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ExampleExample
#include
#include
double average(double v1 , double v2,...); /* Function prototype
*/
int main(void)
{
double Val1 = 10.5, Val2 = 2.5;int num1 = 6, num2 = 5;
long num3 = 12, num4 = 20;
printf("\n Average = %lf", average(Val1, 3.5, Val2, 4.5,
0.0));
printf("\n Average = %lf", average(1.0, 2.0, 0.0));
printf("\n Average = %lf\n", average( (double)num2,
Val2,(double)num1,
(double)num4,(double)num3, 0.0));return 0;
}
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