alt Hacker NewsLong time ago I wrote C. Could anyone fill me in why the first code snippet is arg parsing the way it is?
int main(int argc, char* argv[]) {
if (argc > 1) {
char\* r_loc = strchr(argv[1], 'r');
if (r_loc != NULL) {
ptrdiff_t r_from_start = (r_loc - argv[1]);
if (r_from_start == 1 && argv[1][0] == '-' && strlen(r_loc) == 1) {
in_reverse = 1;
}
}
}
...
Why not
if (argc > 1 && strcmp(argv[1], "-r") == 0) {
in_reverse = 1;
for example?
Replies
I suspect it was adopted from a bigger snippet that had support for parsing things like "-abc" as "-a -b -c", etc.
Not to mention the potential signed integer overflow in (*right - *left) and (*left - *right), which is undefined behavior. And even if you rely on common two's complement wraparound, the result may be wrong; for example, (INT_MAX-(-1)) should mathematically yield a positive value, but the function will produce INT_MIN, which is negative.
And then we have this "modern" way of spelling pointers, "const int* right" (note the space). In C, declaration syntax mirrors use, so it should be "const int *right", because "*right" is a "const int".
I feel too old for this shit. :(
It doesn't even make sense to use strchr for determining the position of 'r', when the code checks that the position of '-' is at index 0.
Your solution is perfectly fine. Even if you don't have access to strchr for some reason, the original snippet is really convoluted.
You could just write (strlen(argv[1]) > 1 && argv[1][0] == '-' && argv[1][0] == 'r') if you really want to.