Trouble with C Code for Case-Insensitive Substring Removal in a String

Question

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

int erase_once(char *input_string, const char *substring, int case_sensitive) {
    size_t string_length = strlen(input_string);
    size_t substring_length = strlen(substring);

    if (string_length < substring_length || substring_length == 0) return 0;

    size_t i;
    for (i = 0; i < string_length - substring_length + 1; i++) {
        int match_found = 1;

        for (size_t j = i; j < i + substring_length; j++) {
            if ((case_sensitive == 0 &&
                 tolower(input_string[j]) != tolower(substring[j-i])) ||
                input_string[j] != substring[j-i]) {
                match_found = 0;
                break;
            }
        }

        if (!match_found) continue;

        for (; i < string_length - substring_length; i++) {
            input_string[i] = input_string[i + substring_length];
        }
        input_string[i] = '\0';

        return 1;
    }

    return 0;
}

int erase(char *input_string, const char *substring, int case_sensitive) {
    int count;
    for (count = 0; erase_once(input_string, substring, case_sensitive); count++);
    return count;
}

int main(void) {
    char main_string[] = "abcdef cde AbCDE";
    const char *substring_to_erase = "abc";

    erase(main_string, substring_to_erase, 0);
    printf("%s\n", main_string);

    return 0;
}

I tryed to make it case sensitive by putting the variable int case_sensitive; and when that wariable is 0 it is not sensitive and when it is 1 it is case sensitive so for example: for input "abcdef cde AbCDE" and substring "abc" if it is 1 it should return -"def cde AbCDE"; and for the same input and case_sensitive set to 0 it should return "def cde DE" another example is for string xYXyXYXY and substring xy and sensitive set to 0 it should return an empty string

but it doesnt, can you help me find the mistake?

Answer 1

Split the task into smaller bits

int strneq(const char *s1, const char *s2, size_t n, int cs)
{
    char c1 = 0, c2 = 0;
    while(n-- && *s1 && *s2)
    {
        if(cs)
        {
            c1 = *s1;
            c2 = *s2;
        }
        else
        {
            c1 = tolower(*s1);
            c2 = tolower(*s2);
        }
        if(c1 != c2) break;
        s1++;
        s2++;
    }
    return !(c1 == c2);
}

char *mystrstr(const char *s, const char *find, int cs)
{
    size_t slen = strlen(s);
    size_t flen = strlen(find);
    char *result = NULL;
    if(slen >= flen)
    for(size_t index = 0; index <= slen - flen; index++)
    {
        if(!strneq(s + index, find, slen - index  + 1, cs))
        {
            result = (char *)(s + index);
            break;
        }
    }
    return result;
}

char *strrem(char *haystack, const char *needle, int cs)
{
    size_t nlen = strlen(needle);
    size_t hlen = strlen(haystack);
    char *current;
    while((current = mystrstr(haystack, needle, cs)))
    {
        while((*current = *(current + nlen))) current++;
    }
    return haystack;
}

int main(void)
{
    char h[] = "abcdef cde AbCDE";
    char *n = "abc";

    printf("'%s'\n", strrem(h,n,0));
}

https://godbolt.org/z/M7bh8Pq7a

Answer 2

you have just forget to check if case_sensitive==1, other wise it will always the second half of your 'if condition' will be checked and considered. this is the line you need to edit

if ((case_sensitive == 0 &&
                 tolower(input_string[j]) != tolower(substring[j-i])) ||
                (case_sensitive == 1 &&
                input_string[j] != substring[j-i]))

note: you have complicated the solution too much, and your code isn't clean enough, those tricks will help you to identify any problem and make it easy for you to debug

Answer 3

Everything inside 1 function:

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

int erase(char* input_string, const char* substring, int case_sensitive) {
    int len1 = strlen(input_string),
        len2 = strlen(substring);

    if (len1 < len2 || len1 < 0) return 0;

    int eraseCount = 0,
        N = len1 - len2 + 1;
    
    for (int i = 0; i < N;) {
        int found = 1;
        
        for (int j = 0; j < len2; j++) {
            char c1 = input_string[i + j], c2 = substring[j];
            
            if(( case_sensitive && tolower(c1) != tolower(c2)) || //case_sensitive == 0 - false, otherwise true (any value)
               (!case_sensitive && c1 != c2)) {
                    found = 0;
                    i += j;
                    break;
            } 
        }
        
        if(found) {
            eraseCount++;
            
            for(int j = i; j < N; j++)
                input_string[j] = input_string[j + len2]; //move left
            for(int j = N + len2 - 2; j >= N - 1; j--)
                input_string[j] = 0; //removed
            
            N -= len2;
        } else i++;
    }
    
    return eraseCount;
}

void test1(){
    char main_string[] = "abcdef cde AbCDE";
    const char *substring_to_erase = "abc";
    erase(main_string, substring_to_erase, 0);
    printf("String: \"%s\"\n", main_string);
}

void test2(){
    char main_string[] = "xYXyXYXY";
    const char *substring_to_erase = "xy";
    erase(main_string, substring_to_erase, 1);
    printf("String: \"%s\"\n", main_string);
}

int main(void) {
    test1();
    test2();
    return 0;
}

Result:

String: "def cde AbCDE"
String: ""


...Program finished with exit code 0
Press ENTER to exit console.