Question

I am currently working on writing strstr from scratch. In my code, I am indexing a string and I eventually need to save a particular point on the string using another pointer. Here is the section of the code that I am struggling with:

char *save_str;
for(int i=0;i<length_str1; i++)
{
    if(str1[i]==str2[0])
    {
        *save_str=str[i];

However, it is telling me that I cannot do this. How can I have a pointer point to a particular character in an index?

Answer 1

Quick Practical Answer

save_str = &str[i];

Extended Descriptive Boring Answer

There is a feature in “pure c” and “c++” about arrays and pointers.

When a programmer wants the address of the full array, or the first item, the “&” operator is not required, even considered as an error or warning by some compilers.

char *myptr = NULL;
char myarray[512];

strcpy(myarray, "Hello World");

// this is the same:
myptr = myarray;

// this is the same:
myptr = &myarray[0];

When a programmer wants the address of a particular item, then the “&” operator is required:

save_str = &str[i];

I read somewhere, that, these feature was added, in purpouse.

Many developer avoid this, and use pointer arithmetics, instead:

...

char *save_str;
...

// "&" not required
char *auxptr = str1;

for(int i=0; i < length_str1; i++)
{
    // compare contents of pointer, not pointer, itself
    if(*auxptr == str2[0])
    {
        *save_str = *auxptr;
    }

    // move pointer to next consecutive location
    auxptr++;
}

...

Personally, I wish, “&” should be use always, and avoid confusion.
Cheers.