How to access command-line arguments in C?

Accessing Command-Line Arguments in C

In the C programming language, you can access command-line arguments passed to your program when it is executed. These arguments are typically used to provide input data or configuration options to the program.

Understanding Command-Line Arguments

When you run a C program from the command line, the operating system passes two pieces of information to the program:

1. argc (argument count): This is an integer value that represents the number of command-line arguments, including the program name itself.

2. argv (argument vector): This is an array of strings, where each string represents a command-line argument. The first element, argv[0], is typically the name of the program being executed.

Here's an example of how the command-line arguments are structured:

In this example, the program is executed with three command-line arguments, so argc is 4 (including the program name).

Accessing Command-Line Arguments

To access the command-line arguments in your C program, you need to declare the main() function with the appropriate parameters:

int main(int argc, char *argv[]) {
    // Your code here
    return 0;
}

Here's an example of how you can use the argc and argv parameters to access the command-line arguments:

#include <stdio.h>

int main(int argc, char *argv[]) {
    printf("Number of command-line arguments: %d\n", argc);

    for (int i = 0; i < argc; i++) {
        printf("Argument %d: %s\n", i, argv[i]);
    }

    return 0;
}

If you save this code in a file named command_line_args.c and compile it with a C compiler (e.g., gcc command_line_args.c -o command_line_args), you can run the program with command-line arguments like this:

./command_line_args arg1 arg2 arg3

The output will be:

Number of command-line arguments: 4
Argument 0: ./command_line_args
Argument 1: arg1
Argument 2: arg2
Argument 3: arg3

As you can see, the program can access the command-line arguments and print them out.

Real-World Example

Imagine you have a program that calculates the area of a rectangle. You can use command-line arguments to pass the length and width of the rectangle to the program:

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[]) {
    if (argc != 3) {
        printf("Usage: %s <length> <width>\n", argv[0]);
        return 1;
    }

    int length = atoi(argv[1]);
    int width = atoi(argv[2]);
    int area = length * width;

    printf("The area of the rectangle is: %d\n", area);
    return 0;
}

In this example, the program expects two command-line arguments: the length and width of the rectangle. If the correct number of arguments is not provided, the program prints a usage message and returns an error code. Otherwise, it calculates the area and prints the result.

By using command-line arguments, you can make your C programs more flexible and reusable, as users can provide input data or configuration options without modifying the source code.