C and Segmentation Faults (strcmp/fclose)

Seguer

Hey guys,

In desperation turn we to H/A!

I have a C assignment (not going to get you guys to do it for me :P) that is causing me headaches; I'm using fgets to get lines from a file (which works fine), but if I try to strcmp the line that results from that, I get a segmentation fault. Unless I printf the line first. Then, upon trying to close the file using fclose I get another fault, even after adding an if statement to check that the file pointer is not null!

Help me, H/A!

falsedef

Need to see some code. How are you allocating the cstrings? You probably failed to allocate space correctly.

Seguer

FILE* packets = openFile(file); //openFile just uses fopen and checks for NULL etc
char line[MAX_CHARS_TO_READ]; //space of 100
fgets(line, MAX_CHARS_TO_READ, packets)


EDIT:

strcmp stuff:

char *messageID;
messageID = strtok(cp, ":");

if (strcmp(messageID, "END\n"))

{

return 1;

}




EDIT: SOLVED It was strcpy causing it. Argh.

theSquid

Isn't it safer to use strncmp instead of strcmp? It won't solve the problem, but it's good practice (prevents buffer overflows, which *may* be the problem) and it might at least prevent the segfault.

EDIT: As well, strncpy.

Seguer

Alright well rather than start a new thread:

Does anyone know how to declare a pointer to a pointer to a struct, so that I can edit the values in the struct? I have plenty of line* start working, but how do I do that with line** start, etc?

CKyle

struct myStructure **p;
// assign stuff

(*p)->field = value;
// or (**p).field = value;

Did that help?

Seguer

I'll have to try it later, but how would I then edit the values in (**p)?

Smasher

I think there's some sort of misunderstanding going on. Why do you need a pointer to a pointer to a struct to change the values of the variables inside it?

There are times when pointers to pointers to things are appropriate (multidimensional arrays, for example), but in this case I suspect you're unintentionally overcomplicating things. What exactly are you attempting to do?