strcat() causing segment fault?

[freestyle12]

Hey i've been trying to get this to work for a while now but nothing i do fixe it.
causes a seg fault at strcat.
Here is the code snippet:

int i=1;
char *opt = " ";
char s = '-';
 
if((argc>1) && s==arg[i][0]){
    strcat(opt, arg[i]);
}

...

argc/arg[] recieved in command line.

Any advice is appreciated!

[horace1]

in the following statement " " is a constant

char *opt = " ";
 

so you cannot use it as a destination in

    strcat(opt, arg[i]);

try

char opt[10] = " ";

making sure there is sufficent room in the array to receive the characters