fscanf and pointers

[Michael Beuwer]

Hey,

I need to adapt an existing c program and have to read out some values and then put them back in. Reading out the values works fine, but reading them in fails. Does anyone know how I can do this, I think it has something to do with structures, but I don't know anything about them. Here is wat I have:

ssprofileout=fopen("ssprofile.dat","a"); /* writes a file named ssprofile.dat with i, x[i] and h[i] */
for (i=istart; i<iend; i++) {
if ((d.e[i] > 0. || d.e[i+50] > 0.) || (d.e[i] > 0. || d.e[i-50] > 0.))
fprinf(ssprofileout,"%i %g %g\n", i,d.x[i],d.h[i]); }
fclose(ssprofileout);

this is the part that works, it gives three arrays. Now I want to put these arrays back into the program by doing this

case SSPROFILE:
ssprofilein=fopen("ssprofile.dat","r");
 
for(i=0; i<(iend-istart); i++) {
fscanf(ssprofilein,"%i %g %g",i,&d.x[i],&d.h[i]);
d->h[i]=d.h[i];
d->x[i]=d.x[i];
} 
fclose(ssprofilein);
 

This obviously doens't work with pointers.. how could I change this in order to makes this work?

Beuwer

[weaknessforcats]

It appears this has nothing o do with structures or pointers. What it does have to do wih is that any data written back to a file as an update must be written in preciselythe eaxct locaion it cam from. That means a) you need to know the file layout and you need to put your update at a precise locaion based on that layout.

so if you know an integer was located 36 bytes from the start of the file and occupies 4 bytes, then yur update must be written at that exact location.

Research seek() and tell(). Examples showing use of seek() and tell() frequenty include one on how to update a file.

[Michael Beuwer]

The program is really big and complex, so I don't know how to find the exact location based on the lay-out, but the errors the program gives are:

error: request for member âxâ in something not a structure or union
error: request for member âhâ in something not a structure or union

in the second c part of my question lines 5,6 and 7..

I don't know if this may give you some more information, because I still don't know what to do

[Banfa]

Take line 6

d->h[i]=d.h[i];

d can not possibly be a structure and a pointer to a structure (actually not quite true in C++ for example iterators can act as both), which is it and what is the purpose of this statement.

[Michael Beuwer]

d.h[i] is the output, and the program makes a new array which is calles d->h[i], so I wanted to assign the value of d.h[i] to d->h[i]

[weaknessforcats]

Are you able to post the declaration for d? When you see d.something, then d is a variable of struct or class whereas d->something means d is an address. Usually two things cannot have the same name unless a)it's C++ and b)there is an overload of the -> operator.

I need to see a bit more.