Sams Teach Yourself C++ in 21 Days

LISTING17.19 Using Command-line Arguments

0: //Listing 17.19 Using Command-line Arguments

1: #include <iostream>

2: int main(int argc, char **argv)

3: {

4: std::cout << “Received “ << argc << “ arguments...\n”;

5: for (int i=0; i<argc; i++)

6: std::cout << “argument “ << i << “: “ << argv[i] << std::endl;

7: return 0;

8: }

TestProgram Teach Yourself C++ In 21 Days

Received 7 arguments...

argumnet 0: TestProgram

argument 1: Teach

argument 2: Yourself

argument 3: C++

argument 4: In

argument 5: 21

argument 6: Days

OUTPUT

632 Day 17

You must either run this code from the command line (that is, from a DOS

box) or you must set the command-line parameters in your compiler (see

your compiler documentation).

NOTE

The function main()declares two arguments:argcis an integer that contains the

count of command-line arguments, and argvis a pointer to the array of strings.

Each string in the array pointed to by argvis a command-line argument. Note that argv

could just as easily have been declared as char *argv[]or char argv[][]. It is a mat-

ter of programming style how you declare argv; even though this program declared it as

a pointer to a pointer, array offsets were still used to access the individual strings.

On line 4,argcis used to print the number of command-line arguments: seven in all,

counting the program name itself.

On lines 5 and 6, each of the command-line arguments is printed, passing the null-termi-

nated strings to coutby indexing into the array of strings.

A more common use of command-line arguments is illustrated by modifying Listing

17.18 to take the filename as a command-line argument, as shown in Listing 17.20.

ANALYSIS