参数中的命令行分配

Question

Is it possible to make command like arguments like below?

./exe FROM_FILE=true 

Here in this case, how I expect in the program is, when FROM_FILE value is true, I wil take data from file and if false, I can take standard values. The other alternatives I find for the purpose is to use

1. -options
2. Simply pass arguments. But in this case I have to worry about the order of arguments.

This one just came to mind when doing a makefile.

$>cat makefile
exe     :
        echo ${FROM_FILE}
$>make FROM_FILE=true
echo true
true
$>

Answer 1

You can do

FROM_FILE=true ./exe

and then read the FROM_FILE environment variable from inside the app with the environ pointer or getenv() . See http://linux.die.net/man/7/environ

Answer 2

EDIT : The more I think about it, the less a good idea it seems to break with common command line interface conventions. maybe you should read this: http://www.gnu.org/prep/standards/html_node/Command_002dLine-Interfaces.html

have you tried environment variables?

you can do

FROM_FILE=true ./exe

and in exe.c:

[...]
char *file = getenv("FROM_FILE");
if (file == NULL)
  *file = DEFAULT;
[...]

alternatively, for a more GNU-ish approach to command line interfaces, have a look at getopt, or argp. ( http://www.gnu.org/software/libc/manual/html_node/Parsing-Program-Arguments.html#Parsing-Program-Arguments )

Answer 3

Possible? Well, since make apparently does it (I haven't tried it myself), it's obviously possible . It might trip up some people because it's certainly an unusual syntax, though.

What you'd want to do then is probably to iterate over argv[] , find any parameters on the form something=something , and do your magic. Maybe even zero them out after you are done with them, and then do something more normal like handing over the grunt work to getopt or a similar library.

One thing to consider, especially if you want this to be generic, is what to do when someone passes a file name to your application that contains a = , expecting that file name to be opened, processed or whatever it is your application does for a living.

Answer 4

Of course it is possible! Something like this (untested):

int main(int argc, char **argv)
{
    int FROM_FILE = 0;
    const char *FROM_FILE_key = "FROM_FILE";
    int i;
    /* Iterate through all the arguments. */
    for (i = 1; i < argc; ++i)
    {
        /* Look for the '='. If not there, skip this argument. */
        char *eq = strchr(argv[i], '=');
        if (!eq)
            continue;

        /* Compare the key. If not what we want, skip it. */
        if (strncmp(argv[i], FROM_FILE_key, strlen(FROM_FILE_key)) != 0)
            continue;

        /* Parse the value. You probably want to make this more flexible 
          (true, 1, yes, y...)*/
        if (strcmp(eq+1, "true") == 0)
            FROM_FILE = 1;
    }

    printf("FROM_FILE=%s", FROM_FILE? "true" : "false");
}