CODEWITHSUNDEEP
c
gaffcz
gaffcz

Reputation: 3479

Compare two strings - get right part of the longer one

I have two strings, e.g.:

How to do something like str1 - str2 to get the dddeee substring?

Upvotes: 1

Views: 144

Answers (5)

Susam Pal
Susam Pal

Reputation: 34284

Since you have clarified that str2 is a prefix of str1, you can get the pointer to the extra part in str2 simply with the operation:

str1 + strlen(2);

For example, to print the "dddeee" part of your string:

printf("%s\n", str1 + strlen(str2));

How this works is simple. str1 + strlen(str2) is a pointer that is strlen(str2) N characters away from the beginning of the string pointed to be str1. strlen(str2) returns the number of characters in the second string and you skip those many characters in the first string and reach the extra part.

Upvotes: 1

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272657

If str2 is guaranteed to be a prefix of str1, then this will suffice:

const char *str3 = &str1[strlen(str2)];

which is equivalent to this: (as @James points out in the comments)

const char *str3 = str1 + strlen(str2);

Of course, str3 is just a pointer into one of the original strings. If the contents of the original string changes, then so will your result. So you may want to create a copy, using malloc() and strcpy() (and then free() at some point).

Upvotes: 5

hmjd
hmjd

Reputation: 122001

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

int main()
{
    char a[] = "aaaabbbbbdddeee";
    char b[] = "aaaabbbbb";

    const char* start = strstr(a, b);
    if (start)
    {
        printf("%s\n", a + strlen(b));
    }

    return 0;
}

Upvotes: 1

Pih
Pih

Reputation: 2278

str3 will contain a copy of the prefix:

str1 = "aaabbbcccdddeee"
str2 = "aaabbbccc"

size_t length = strlen1 - strlen2; 
char* str3 = calloc(sizeof(char), length + 1);

memcpy(str3, str1+strlen(str2), length);

Upvotes: 1

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726809

This will skip the common prefix of two strings:

char* suffix(const char* prefix, const char* str) {
    while (*prefix && *str && *prefix == *str) {
        prefix++;
        str++;
    }
    return str;
}

For example, if you pass "AAB" and "AACC", this would return "CC".

Upvotes: 2

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