Command Line Arguments in C
The most important function of C is the main() function. It is mostly defined with a return type of int and without parameters.
int main() { ... }
We can also give command-line arguments in C. Command-line arguments are the values given after the name of the program in the command-line shell of Operating Systems. Command-line arguments are handled by the main() function of a C program.
To pass command-line arguments, we typically define main() with two arguments: the first argument is the number of command-line arguments and the second is a list of command-line arguments.
Syntax
int main(int argc, char *argv[]) { /* ... */ } or int main(int argc, char **argv) { /* ... */ }
Here,
- argc (ARGument Count) is an integer variable that stores the number of command-line arguments passed by the user including the name of the program. So if we pass a value to a program, the value of argc would be 2 (one for argument and one for program name)
- The value of argc should be non-negative.
- argv (ARGument Vector) is an array of character pointers listing all the arguments.
- If argc is greater than zero, the array elements from argv[0] to argv[argc-1] will contain pointers to strings.
- argv[0] is the name of the program , After that till argv[argc-1] every element is command -line arguments.
For better understanding run this code on your Linux machine.
Example
The below example illustrates the printing of command line arguments.
C
// C program named mainreturn.c to demonstrate the working // of command line arguement #include <stdio.h> // defining main with arguments int main( int argc, char * argv[]) { printf ( "You have entered %d arguments:\n" , argc); for ( int i = 0; i < argc; i++) { printf ( "%s\n" , argv[i]); } return 0; } |
Output
You have entered 4 arguments: ./main Beginner for Beginner
for Terminal Input
$ g++ mainreturn.cpp -o main $ ./main Beginner for Beginner
Note: Other platform-dependent formats are also allowed by the C standards; for example, Unix (though not POSIX.1) and Microsoft Visual C++ have a third argument giving the program’s environment, otherwise accessible through getenv in stdlib.h. Refer C program to print environment variables for details.
Properties of Command Line Arguments in C
- They are passed to the main() function.
- They are parameters/arguments supplied to the program when it is invoked.
- They are used to control programs from outside instead of hard coding those values inside the code.
- argv[argc] is a NULL pointer.
- argv[0] holds the name of the program.
- argv[1] points to the first command line argument and argv[argc-1] points to the last argument.
Note: You pass all the command line arguments separated by a space, but if the argument itself has a space, then you can pass such arguments by putting them inside double quotes “” or single quotes ”.
Example
The below program demonstrates the working of command line arguments.
C
// C program to illustrate // command line arguments #include <stdio.h> int main( int argc, char * argv[]) { printf ( "Program name is: %s" , argv[0]); if (argc == 1) printf ( "\nNo Extra Command Line Argument Passed " "Other Than Program Name" ); if (argc >= 2) { printf ( "\nNumber Of Arguments Passed: %d" , argc); printf ( "\n----Following Are The Command Line " "Arguments Passed----" ); for ( int i = 0; i < argc; i++) printf ( "\nargv[%d]: %s" , i, argv[i]); } return 0; } |
Output in different scenarios:
1. Without argument: When the above code is compiled and executed without passing any argument, it produces the following output.
Terminal Input
$ ./a.out
Output
Program Name Is: ./a.out No Extra Command Line Argument Passed Other Than Program Name
2. Three arguments: When the above code is compiled and executed with three arguments, it produces the following output.
Terminal Input
$ ./a.out First Second Third
Output
Program Name Is: ./a.out Number Of Arguments Passed: 4 ----Following Are The Command Line Arguments Passed---- argv[0]: ./a.out argv[1]: First argv[2]: Second argv[3]: Third
3. Single Argument: When the above code is compiled and executed with a single argument separated by space but inside double quotes, it produces the following output.
Terminal Input
$ ./a.out "First Second Third"
Output
Program Name Is: ./a.out Number Of Arguments Passed: 2 ----Following Are The Command Line Arguments Passed---- argv[0]: ./a.out argv[1]: First Second Third
4. A single argument in quotes separated by space: When the above code is compiled and executed with a single argument separated by space but inside single quotes, it produces the following output.
Terminal Input
$ ./a.out 'First Second Third'
Output
Program Name Is: ./a.out Number Of Arguments Passed: 2 ----Following Are The Command Line Arguments Passed---- argv[0]: ./a.out argv[1]: First Second Third
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