Command Line Arguments in C

By: Rajesh P.S.

In C, command-line arguments are a way to pass parameters to a C program when it is executed from the command line. These arguments are provided by the user when running the program and are used to customize the behavior of the program. Command-line arguments are typically provided after the program name in the command line.

Main Function Signature

In C, the main function is the entry point of the program. It can take two arguments: argc and argv.

argc: The number of command line arguments, including the program name.
argv: An array of pointers to strings, where each string is a command line argument.

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

Accessing Command-Line Arguments

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You can access command-line arguments through the argv array. The first element (argv[0]) is the program's name, and the subsequent elements contain the user-provided arguments.

#include <stdio.h> int main(int argc, char *argv[]) { printf("Program name: %s\n", argv[0]); // Check if there are additional arguments if (argc > 1) { printf("Arguments provided:\n"); for (int i = 1; i < argc; i++) { printf("Argument %d: %s\n", i, argv[i]); } } else { printf("No additional arguments provided.\n"); } return 0; }

When you run the program with ./myprogram arg1 arg2, the output will be:

Program name: ./myprogram Arguments provided: Argument 1: arg1 Argument 2: arg2

Multiple command line arguments

You can also pass multiple command line arguments to a program. For example, the following program takes two command line arguments and prints the sum of the two numbers to the console:

#include <stdio.h> int main(int argc, char *argv[]) { if (argc != 3) { printf("Usage: %s <number1> <number2>\n", argv[0]); return 1; } int number1 = atoi(argv[1]); int number2 = atoi(argv[2]); int sum = number1 + number2; printf("The sum of %d and %d is %d\n", number1, number2, sum); return 0; }

To compile and run this program, you would use the following commands:

gcc -o sum_test sum_test.c

./sum_test 10 20

//Output: The sum of 10 and 20 is 30

Converting Command-Line Arguments

The arguments in argv are stored as strings, so if you need to use them as other data types, you'll need to convert them. For example, converting a string to an integer:

#include <stdio.h> #include <stdlib.h> int main(int argc, char *argv[]) { if (argc == 2) { int number = atoi(argv[1]); // Convert the second argument to an integer printf("Integer value: %d\n", number); } else { printf("Please provide one integer argument.\n"); } return 0; }

When you run the program with ./myprogram 42, the output will be:

Integer value: 42

Error Handling

It's essential to validate and handle command-line arguments correctly. Check argc to ensure the correct number of arguments are provided, and check the content of argv to ensure they meet your program's requirements. If they don't, provide appropriate error messages.

#include <stdio.h> int main(int argc, char *argv[]) { if (argc != 2) { printf("Usage: %s <filename>\n", argv[0]); return 1; // Return an error code } else { // Process the file specified in argv[1] printf("Processing file: %s\n", argv[1]); // Add your file processing code here } return 0; }

When you run the program with ./myprogram, it will display a usage message. When you run it as ./myprogram file.txt, it will process the file.

Conclusion

Command-line arguments are provided by users when running a program and are accessible through the argc and argv parameters in the main function. argc represents the number of arguments, while argv is an array of strings containing those arguments, allowing programs to be customized and configured with user input from the command line.

Next > Type Casting in C

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