1. Command-line arguments CS 201 Fundamental Structures of Computer Science

2. Introduction A command-line argument is the information that follows the name of the program on the command line of the operating system Command-line arguments are used to pass information into a program when you run it –They facilitate the use of your program in batch files –They give a professional appearance to your program

3. Introduction C++ defines two built-in parameters to main() –They receive the command line arguments –Their names are argc and argv The names of the parameters are arbitrary. However, argc and argv have been used by convention for several years. –They are optional

4. int main( int argc, char *argv[] ) argc is an integer –Holds the number of arguments on the command line –Since the name of the program always corresponds to the first argument, it is always at least 1

5. int main( int argc, char *argv[] ) argv is a pointer to an array of character pointers. –Each character pointer in the argv array corresponds a string containing a command-line argument argv[0] points the name of the program, argv[1] points to the first argument, argv[2] points to the second argument, … –Each command-line argument is a string If you want to pass numerical information to your program, your program should convert the corresponding argument into its numerical equivalent –Each command-line argument must be separated by spaces or tabs Commas, semicolons, and the like are not valid argument separators

6. #include using namespace std; int main( int argc, char *argv[] ){ cout << "Hello "; for (int i = 1; i < argc; i++) cout << argv[i] << " "; cout << "! " << endl; return 0; } [cgunduz@knuth cgunduz]$ g++ prog1.cpp –o exe_1 [cgunduz@knuth cgunduz]$./exe_1 Cigdem Gunduz Hello Cigdem Gunduz ! [cgunduz@knuth cgunduz]$./exe_1 Cigdem Gunduz Demir Hello Cigdem Gunduz Demir !

7. Passing numeric command-line arguments All command-line arguments are passed to the program as strings –Your program should convert them into their proper internal format For that, C++ supports standard library functions most commonly used ones are: –atof() : converts a string to a double and returns the result –atoi() : converts a string to a int and returns the result –atol() : converts a string to a long int and returns the result Each of these functions –Expects a string containing a numeric value as an argument –Uses the header

8. #include using namespace std; int main( int argc, char *argv[] ){ if (argc != 4){ cout << "Usage: \n\t"; cout << "1. Integer (0) or double (1) division\n\t"; cout << "2. Operand 1\n\t3. Operand 2\n\n"; exit(1); } if (atoi(argv[1]) == 0){ int a = atoi(argv[2]); int b = atoi(argv[3]); cout << a << "\\" << b << " = " << a / b << endl; } else{ double a = atof(argv[2]); double b = atof(argv[3]); cout << a << "\\" << b << " = " << a / b << endl; } return 0; }

9. [cgunduz@knuth cgunduz]$ g++ prog2.cpp -o exe_2 [cgunduz@knuth cgunduz]$./exe_2 Usage: 1. Integer (0) or double (1) division 2. Operand 1 3. Operand 2 [cgunduz@knuth cgunduz]$./exe_2 0 5 3 5\3 = 1 [cgunduz@knuth cgunduz]$./exe_2 1 5 3 5\3 = 1.66667 [cgunduz@knuth cgunduz]$./exe_2 0 8.2 2.9 8\2 = 4 [cgunduz@knuth cgunduz]$./exe_2 1 8.2 2.9 8.2\2.9 = 2.82759