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Martina
Martina

Reputation: 19

How to find if a char array exist in another char array without using string library?

I have two char arrays char search_array[8] and input_array[30] and I'm getting the characters by using getchar, but I want to find if the search array exists in input array without using string library.

Example:

search array: hello

input array hello, how are you

Upvotes: 0

Views: 315

Answers (2)

chqrlie
chqrlie

Reputation: 144740

The obvious solution for your goal is to use the standard library's strstr function.

Since you are not allowed to use the string library, you should write your own version of strstr and use that.

Here is a simple yet conforming implementation:

char *my_strstr(const char *s1, const char *s2) {
    for (;;) {
        for (size_t i = 0;; i++) {
            if (s2[i] == '\0')
                return (char *)s1;
            if (s1[i] != s2[i])
                break;
        }
        if (*s1++ == '\0')
            return NULL;
    }
}

You then use this function this way:

    if (my_strstr(input_array, search_array)) {
        printf("string was found\n");
    } else {
        printf("string was not found\n");
    }

Upvotes: 1

Linguist Lamer
Linguist Lamer

Reputation: 21

You need some string comparison loop, like that of which you can find in strcmp or strcspn. This is assuming you use a terminal value like C strings; if you use some length field you'll need to make adjustments to the loops to account for those clearly. Here are some examples:

int strcmp(char const *x, char const *y) {
    while (*x && *x == *y) {
        x++;
        y++;
    }
    return ((unsigned)*x > (unsigned)*y) - ((unsigned)*x < (unsigned)*y);
}

size_t strcspn(char const *x, char const *y) {
    char const *x_ = x;
    while (*x_) {
        for (char const *y_ = y; *y_; y_++) {
            if (*x_ == *y_)
                return x_ - x;
        }
        x_++;
    }
    return x_ - x;
}

Upvotes: 2

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