Question

I am still learning C and I’m having some trouble figuring out how to handle this. Well, I have two structs:

struct myStruct {
    ...
    struct myString *text[5];
    ...
} allStructs;

struct myString {
    char part[100];
};

The objective is to have allStruct[n] point to 5 different parts of a text divided into lines of 100 chars each. So I allocate the space:

allStructs = calloc(n, sizeof(allStructs));

Then, assume that I have a filled char text[500] that I want to divide into 5 parts, and have allStructs[n].text[n].part point at a given part of the text. Can anyone help me with how I proceed?

Answer 1

Short answer: you can not with this because you have not consider the ‘\0’ character to terminate each string.

Longer answer:
Change structs like that to have more flexibility:

struct myStruct {
   struct myString *text;
}
struct myString {
   char *part;
}

The allocation should be:

struct myStruct *allStruct = calloc(n, sizeof(struct myStruct));

So you have a pointer/array on n struct myStruct.

Then initialize all members of allStruct;

for( i=0; i<n; ++i )
{
   allStruct[i].text = calloc(5, sizeof(myString));
   // Following for only needed if you want new strings by using the strncpy (see above)
   for( y=0; y<5; ++y )
   {
      allSTruct[i].text[y].part = calloc(101, sizeof(char));
   }
}

Now you have all vars initialized.

To copy your 500-chars long string into allStruct[n]:

for( i=0; i<5; i++ )
{
   allStructs[n].text[i].part = &text[i*100]; // If you want to point on the existing string
   // OR
   strncpy(allStructs[n].text[i].part, &text[i*100], 100); // If you want to have new strings

   // In all case, terminate the string with '\0'
   allStructs[n].text[i].part[100] = '\0';
}

This should work.