Replace Part of a String With Another String

Replace part of a string with another string

There's a function to find a substring within a string (find), and a function to replace a particular range in a string with another string (replace), so you can combine those to get the effect you want:

bool replace(std::string& str, const std::string& from, const std::string& to) {
    size_t start_pos = str.find(from);
    if(start_pos == std::string::npos)
        return false;
    str.replace(start_pos, from.length(), to);
    return true;
}

std::string string("hello $name");
replace(string, "$name", "Somename");

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In response to a comment, I think replaceAll would probably look something like this:

void replaceAll(std::string& str, const std::string& from, const std::string& to) {
    if(from.empty())
        return;
    size_t start_pos = 0;
    while((start_pos = str.find(from, start_pos)) != std::string::npos) {
        str.replace(start_pos, from.length(), to);
        start_pos += to.length(); // In case 'to' contains 'from', like replacing 'x' with 'yx'
    }
}

How to replace a part of a string with another substring

Replacing a substring with another is easy if both substrings have the same length:

• locate the position of the substring with strstr
• if it is present, use memcpy to overwrite it with the new substring.
• assigning the pointer with *strstr(m, "on") = "in"; is incorrect and should generate a compiler warning. You would avoid such mistakes with gcc -Wall -Werror.
• note however that you cannot modify a string literal, you need to define an initialized array of char so you can modify it.

Here is a corrected version:

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

int main(void) {
    char m[] = "cat on couch";
    char *p = strstr(m, "on");
    if (p != NULL) {
        memcpy(p, "in", 2);
    }
    printf("%s\n", m);
    return 0;
}

If the replacement is shorter, the code is a little more complicated:

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

int main(void) {
    char m[] = "cat is out roaming";
    char *p = strstr(m, "out");
    if (p != NULL) {
        memcpy(p, "in", 2);
        memmove(p + 2, p + 3, strlen(p + 3) + 1);
    }
    printf("%s\n", m);
    return 0;
}

In the generic case, it is even more complicated and the array must be large enough to accommodate for the length difference:

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

int main(void) {
    char m[30] = "cat is inside the barn";
    char *p = strstr(m, "inside");
    if (p != NULL) {
        memmove(p + 7, p + 6, strlen(p + 6) + 1);
        memcpy(p, "outside", 7);
    }
    printf("%s\n", m);
    return 0;
}

Here is a generic function that handles all cases:

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

char *strreplace(char *s, const char *s1, const char *s2) {
    char *p = strstr(s, s1);
    if (p != NULL) {
        size_t len1 = strlen(s1);
        size_t len2 = strlen(s2);
        if (len1 != len2)
            memmove(p + len2, p + len1, strlen(p + len1) + 1);
        memcpy(p, s2, len2);
    }
    return s;
}

int main(void) {
    char m[30] = "cat is inside the barn";

    printf("%s\n", m);
    printf("%s\n", strreplace(m, "inside", "in"));
    printf("%s\n", strreplace(m, "in", "on"));
    printf("%s\n", strreplace(m, "on", "outside"));
    return 0;
}

Replace part of a string in Python?

>>> stuff = "Big and small"
>>> stuff.replace(" and ","/")
'Big/small'

Replace part of string if another string exists

Can be done with a regex pattern using positive lookbehind with the wanted variable inserted in it:

let str1 = "RHID='1' AND CD_FF='Cartão Crédito'";
const str2 = "'Marca/Modelo'";  // no need to hardcode CD_FF here

const variable = "CD_FF";  // can be taken from anywhere

const pattern = new RegExp(`(?<=${variable}=).*`);
str1 = str1.replace(pattern, str2);

console.log(str1);

Output:

RHID='1' AND CD_FF='Marca/Modelo'

Note that str3 is not needed for anything and also that this code correctly does no replacements if the CD_FF (or whatever is in variable) is not found from the str1.

How to replace part of a String in Java?

Use regex like this :

public static void main(String[] args) {
    String s = "Hello my Dg6Us9k. I am alive";
    String newString=s.replaceFirst("\\smy\\s\\w{7}", "");
    System.out.println(newString);
}

O/P :
Hello. I am alive

replace part of the string in C#

Well, well well

Take your universal method:

        public string Replacement(string input, string replacement)
        {
            string[] words = input.Split(' ');
            string result = string.Empty;

            for (int i = 0; i < words.Length; i++)
            {
                if(words[i].Contains('/'))
                {
                    int barIndex = Reverse(words[i]).LastIndexOf('/') + 1;
                    int removeLenght = words[i].Substring(barIndex).Length;
                    words[i] = Reverse(words[i]);
                    words[i] = words[i].Remove(barIndex, removeLenght);
                    words[i] = words[i].Insert(barIndex, Reverse(replacement));
                    string ToReverse = words[i];
                    words[i] = Reverse(ToReverse);

                    break;
                }
            }

            for(int i = 0; i < words.Length; i++)
            {
                result += words[i] + " ";
            }

            result = result.Remove(result.Length - 1);

            return result;
        }

        public string Reverse(string s)
        {
            char[] charArray = s.ToCharArray();
            Array.Reverse(charArray);
            return new string(charArray);
        }

In reponse to >> I need a universal method to replace any stuff between the slash and the space closest to it

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