When executing the program, you can pass values to the C program from the command line. These values are called command-line parameters , and they are important to the program, especially when you want to control the program from the outside instead of hard-coding these values in the code.
Command line parameters are processed using main() function parameters, where argc refers to the number of parameters passed in, and argv[] is an array of pointers that point to each parameter passed to the program.
The following is a simple example, check whether the command line provides parameters, and perform corresponding actions according to the parameters:
#include <stdio.h> int main( int argc, char *argv[] ) { if( argc == 2 ) { printf("The argument supplied is %s/n", argv[1]); }
else if( argc > 2 )
{ printf("Too many arguments supplied./n"); } else { printf("One argument expected./n"); } }Compile and execute the above code with one parameter, it will produce the following results:
$./a.out testing The argument supplied is testing
Compile and execute the above code with two parameters, it will produce the following results:
$./a.out testing1 testing2 Too many arguments supplied.
Compile and execute the above code without passing any parameters, it will produce the following results:
$./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 parameter, and *argv[n] is the last parameter.
If no parameter is provided, argc will be 1, otherwise, if an argument is passed, argc will be set to 2.
Multiple command line parameters are separated by spaces, but if the parameters themselves contain spaces, the parameters should be placed in double quotation marks "" or single quotation marks" when passing parameters.
Let us rewrite the above example, there is a space, then you can pass this point of view, put them in double quotes or single quotes """".
Let us rewrite the above example and pass a command line parameter placed inside double quotes to the program:
#include <stdio.h> int main( int argc, char *argv[] ) { printf("Program name %s/n", argv[0]); if( argc == 2 )
{ printf("The argument supplied is %s/n", argv[1]); } else if( argc > 2 ) { printf("Too many arguments supplied./n"); }
else { printf("One argument expected./n"); } }Using a simple parameter separated by spaces, enclosed in double quotes, compiling and executing the above code, it will produce the following results:
$./a.out "testing1 testing2" Progranm name ./a.out The argument supplied is testing1 testing2
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