C Command-line arguments

When a program is executed, values can be passed to a C program from the command line. These values are calledCommand-line argumentsThey are important to the program, especially when you want to control the program from outside rather than hard-coding these values in the code.

In C language, command line arguments are a method of obtaining input from the command line, which can be used to pass information to the program when running the program. Command line arguments are passed to the program through the parameters of the main function. The prototype of the main function can be one of the following two forms:

int main(int argc, char *argv[]);

or:

int main(int argc, char **argv);

• argc (argument count): indicates the number of command-line arguments, including the program name itself. Therefore,argcAt least 1.

• argv (argument vector): is a pointer to an array of strings, where each string is a command-line argument. The first element of the array (i.e.,argv[0]) is usually the name of the program. The following elements are the command-line arguments passed to the program.

The following is a simple example that checks whether command line arguments are provided and performs corresponding actions based on the arguments:

Using one argument, compile and execute the above code, it will produce the following result:

$./a.out testing
The argument supplied is testing

Using two arguments, compile and execute the above code, it will produce the following result:

$./a.out testing1 testing2
Too many arguments supplied.

Passing no arguments, compile and execute the above code, it will produce the following result:

$./a.out
One argument expected

It should be noted that,argv[0]stores the name of the program,argv[1]is a pointer to the first command-line argument, and *argv[n] is the last argument. If no arguments are provided, argc will be 1; otherwise, if one argument is passed,argcwill be set to 2.

Multiple command line arguments are separated by spaces, but if the argument itself contains spaces, then when passing arguments you should place the argument inside double quotes "" or single quotes ''. Let's rewrite the above example, there is a space, then you can, from this point of view, put them in double quotes or single quotes "". Let's rewrite the above example to pass a command line argument placed inside double quotes to the program:

Using a simple argument separated by a space, with the argument enclosed in double quotes, compile and execute the above code, it will produce the following result:

$./a.out "testing1 testing2"

Progranm name ./a.out
The argument supplied is testing1 testing2

Use Case

Command-line arguments are useful in many situations, for example:

• Configuration file path
• Mode selection (e.g., debug mode)
• Input file and output file names
• Runtime options and flags (such as-vindicates verbose mode)

Notes

• Command-line arguments are usually strings; if you need to convert them to numeric types, you can use standard library functions such asatoiorstrtol。
• You should always validate and handle command-line arguments to prevent incorrect or malicious input.