C substrings / C string slicing?

Question

Hy everybody! I am trying to write a program that checks if a given string of text is a palindrome (for this I made a function called is_palindrome that works) and if any of it's substrings is a palindrome, and I can't figure out what is the optimal way to do this:

For example, for the string s = "abcdefg" it should first check "a", then "ab", "abc", "abcd" and so on, for each character

In Python this is the equivalent of
s[:1], s[:2], ...      (a, ab, ...)
s[1:2], s[1:3] ...     (b, bc, ...)

What function/method is there that I can use in a similar way in C ?

Answer 1

This slice_str() function will do the trick, with end actually being the end character, rather than one-past-the-end as in Python slicing:

#include <stdio.h>
#include <string.h>

void slice_str(const char * str, char * buffer, size_t start, size_t end)
{
    size_t j = 0;
    for ( size_t i = start; i <= end; ++i ) {
        buffer[j++] = str[i];
    }
    buffer[j] = 0;
}

int main(void) {
    const char * str = "Polly";
    const size_t len = strlen(str);
    char buffer[len + 1];

    for ( size_t start = 0; start < len; ++start ) {
        for ( int end = len - 1; end >= (int) start; --end ) {
            slice_str(str, buffer, start, end);
            printf("%s\n", buffer);
        }
    }

    return 0;
}

which, when used from the above main() function, outputs:

paul@horus:~/src/sandbox$ ./allsubstr
Polly
Poll
Pol
Po
P
olly
oll
ol
o
lly
ll
l
ly
l
y
paul@horus:~/src/sandbox$ 

Answer 2

This is the one liner I use to get a slice of a string in C.

void slice(const char *str, char *result, size_t start, size_t end)
{
    strncpy(result, str + start, end - start);
}

Pretty straightforward. Given you've checked boundaries and made sure end > start.