413C 语言 Command line
Posted alex-bn-lee
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Command-Line Arguments
All the executable programs above have a main(void) program
- more generally, executables take arguments on the command line
- these enter the program via parameters
For example:
prompt$ ./a.out -pre 3
means that:
-
argc refers to the number of arguments, including the program name
-
argc = 3
-
-
argv[] allows access to arguments represented as strings
-
argv[0] is a pointer to the string "./a.out"
-
argv[1] is a pointer to the string "-pre"
-
argv[2] is a pointer to the string "3"
-
Command-line argument processing example 1
Write a program that:
- takes an optional numerical command-line argument 1, 2, 3 or 4
- if the argument is not one of these characters (!), a usage message is printed
切换行号显示
// commarg.c #include <stdio.h> #include <stdlib.h> int main(int argc, char *argv[]) if (argc == 1 || (argc == 2 && atoi(argv[1]) >= 1 && atoi(argv[1]) <= 4)) // we can do something here else printf("Usage: %s [1|2|3|4]\n", argv[0]); return EXIT_SUCCESS;
-
notice that atoi() had to be called to convert the character to a number
- compiling and executing the program:
prompt$ dcc commarg.c prompt$ ./a.out prompt$ ./a.out 1 prompt$ ./a.out 2 prompt$ ./a.out 3 prompt$ ./a.out 4 prompt$ ./a.out 5 Usage: ./a.out [1|2|3|4]
Command-line argument processing example 2
Write a program that:
-
takes an optional command-line switch -reverse
- if the switch is not correct, a usage message is printed
切换行号显示
// commargrev.c #include <stdio.h> #include <stdlib.h> #include <string.h> int main(int argc, char *argv[]) if (argc == 1 || (argc == 2 && !strcmp(argv[1], "-reverse"))) // NOTE: strcmp returns 0 if matches. // we could do something here else printf("Usage: %s [-reverse]\n", argv[0]); return EXIT_SUCCESS;
prompt$ ./a.out prompt$ ./a.out -reverse prompt$ ./a.out rubbish Usage: ./a.out [-reverse]
Makefile
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