**char problems in C

[shawn_drn]

Hello,
I need to write a function as follows:

//return a list of all the names d has
char** ls(directory* dir);

struct directory{
char* name;
int num_of_files;
struct directory *next;
}


My problem is that name could be of any size and d can be of any size and I can't get the dynamic allocation to work for **char. Here is an attempt:

ret = (char**)malloc(sizeof(dir->num_of_files)*sizeof(char*));
for(i=0; i<dir->num_of_files; i++){
ret[i] = malloc(sizeof(char)*sizeof(dir->name));
ret[i] = dir->name;
dir->files = dir->files->next;
}

Hope someone can straighten this out for me and write out how this should be done. Send an email to [email protected]

Thanks

[Sebastiani]

>> ret = (char**)malloc(sizeof(dir->num_of_files)*sizeof(char*));

dir->num_of_files is an int, so sizeof() will return the value of 4 (usually). Just omit that then.

>> ret[i] = malloc(sizeof(char)*sizeof(dir->name));

since dir->name is a pointer, sizeof() will return the size of a pointer, which is 4 (usually). Use strlen(dir->name)+1.

>> ret[i] = dir->name;

That line effectively loses track of the memory you allocated in the previous line of code. Perhaps you meant to use strcpy()?

>> dir->files = dir->files->next;

I didn't see a data member 'files' there, hmmm. Anyhow, be careful when playing with pointers belonging to other data structures. Best bet is to declare a separate 'iterating' pointer, and move through the data that way....

[shawn_drn]

Thanks a lot, I'm able to get it two work now that I use the string copy function. it's off putting because you often see things like

x = "blah";

where x is of type char*