Csh script call C program,arguments issue - c

Question

This the line from the csh script
./model2grd $model -D$nx/$ny/$nz -O$x0/$y0 -I$dx/$dy -L$layer -C$coverage -Avel.dat -Gvel.grd
This is part of the model2grd.c
for (i = 2; i < argc; i++) {
if (argv[i][0] == '-') {
switch (argv[i][1]) {
case 'G':
grdfile = &argv[i][2];
lgrd = TRUE;
break;
case 'C':
cov = &argv[i][2];
lcov = TRUE;
break;
case 'A':
xyzfile = &argv[i][2];
lxyz = TRUE;
break;
case 'D':
sscanf(&argv[i][2],"%d/%d/%d",&nx,&ny,&nz);
break;
case 'I':
sscanf(&argv[i][2], "%lf/%lf", &dx, &dy);
break;
case 'O':
sscanf(&argv[i][2], "%lf/%lf", &xmin, &ymin);
break;
case 'L':
layer = atoi(&argv[i][2]);
break;
case 'N':
nan = (float)atof(&argv[i][2]);
break;
case 'Z':
cvalue = (float)atof(&argv[i][2]);
break;
case 'V':
verbose = TRUE;
break;
default:
break;
}
}
}
Does this mean that it takes with D(nx,ny,nz),with O(xmin and ymin),with L layer and with C coverage?Are Avel.dat and Gvel.grd input files or not?

Answer 1

Avel.dat and Gvel.grd are not input files. Look at the argument parsing again.
switch (argv[i][1]) {
case 'G':
grdfile = &argv[i][2];
lgrd = TRUE;
break;
Consider that with this argument:
-Gvel.grd
In plain English, the switch examines the second character of each argument. In this case -Gvel.grd is the argument, so it looks at the G. Passing that test, the case statement then derives the address of the character that comes immediately after the G within the character string. In other words, the v.
Therefore, the file name is actually vel.grd. You should be able to apply this same logic to the rest of the arguments that follow the same pattern.