[FIXED] Why it returns me segmention fault (core dumbed)?

Issue

After putting two strings, it returns me segmention fault (core dumbed)

I'm running the code with gcc. Valgrind writes that there are no errors. Tried to write code that decrypts text using the Caesar method. First I enter the text to be decoded, and the second text shows how far I need to move the letters in the first text. That is, the distance is selected at which there is more correspondence in letters between the received text and the second entered text. I carefully checked everything, for me it seems that there are really no errors, or I'm just not well versed in working with memory.

Here's example

inputs

xUbbemehbT

XYlloworld

should return

Helloworld

I really don't understand why it returns me that, here is code

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

#define INT_MSG_LEN 50;

enum {NO_ERROR = 0, 
      ERROR_INPUT = 100, 
      ERROR_LEN = 101};

static const char *error_texts[] = { "Error input!", 
                                     "Error lenght"};

void shift(char *msgEnc, char *msg, char *msgRes, char *mainMsg, char *alphabet, int offset);
void report_error(int error);
void print_error(int error);
int get_sameletters(char *msg, char *msgRes, int offset);
int get_letter(char letter, char *alphabet);
int compare(char *msgEnc, char *msg, char *msgRes, char *alphabet, int offset);
char *read_Input_Msg(int *msglen);

int main(int argc, char *argv[])
{
    int ret = NO_ERROR;
    char *msgEnc, *msg, *msgRes, *mainMsg, alphabet[53] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    int msgEncLen, msgLen;

    msgEnc = msg = msgRes = mainMsg = NULL;
    msgEncLen = msgLen = 0;

    msgEnc = read_Input_Msg(&msgEncLen);
    if (msgEnc)
        msg = read_Input_Msg(&msgLen);

    if (msgEnc == NULL || msg == NULL)
        ret = ERROR_INPUT;
    else if (msgEncLen != msgLen)
        ret = ERROR_LEN;
    
    if (ret == NO_ERROR)
        shift(msgEnc, msg, msgRes, mainMsg, alphabet, msgEncLen);
    else
        print_error(ret);

    free(msgEnc);
    free(msg);
    free(msgRes);
    free(mainMsg);
    return ret;
}

void shift(char *msgEnc, char *msg, char *msgRes, char *mainMsg, char *alphabet, int offset)
{//function for decoding text by a defined offset
    int dis;
    dis = compare(msgEnc, msg, msgRes, alphabet, offset);
    for (int i = 0; i<offset-1; ++i){
        if ((msgEnc[i] >= 'a' && msgEnc[i] <= 'z') || (msgEnc[i] >= 'A' && msgEnc[i] <= 'Z')){
            mainMsg[i] = msgEnc[i+dis];
            break;
        }
    }
    for(int i = 0; i<offset-1; ++i)
        printf("%c", mainMsg[i]);
}

void report_error(int error)
{//prints error 
    if (error >= ERROR_INPUT && error <= ERROR_LEN)
        fprintf(stderr, "%s\n", error_texts[error - ERROR_INPUT]);
}

void print_error(int error)
{//what error it is
    switch (error){
        case ERROR_INPUT:
            report_error(ERROR_INPUT);
            break;
        case ERROR_LEN:
            report_error(ERROR_LEN);
            break;
    }
}

int get_sameletters(char *msg, char *msgRes, int offset)
{//gets count of sameletters between two strings
    int sameLetters = 0;
    for (int i = 0; i<offset-1; ++i){
        if (msg[i] == msgRes[i])
            sameLetters++;
    }
    return sameLetters;
}

int get_letter(char letter, char *alphabet)
{   
    int k;
    for (int i=0; alphabet[i]; ++i){
        if (letter == alphabet[i])
            k = i;
    }
    return k;
}

int compare(char *msgEnc, char *msg, char *msgRes, char *alphabet, int offset)
{//calculate a distance between first input string and string what will get after decryption
    int distance, max = 0;
    for (int i = 0; alphabet[i]; ++i){
        for (int j = 0; msgEnc[j]; ++j){
            if ((msgEnc[i] >= 'a' && msgEnc[i] <= 'z') || (msgEnc[i] >= 'A' && msgEnc[i] <= 'Z'))
                msgRes[j] = alphabet[(get_letter(msgEnc[j], alphabet) + i) % 52];
            }
            int sameLetters = get_sameletters(msg, msgRes, offset);
            if (sameLetters > max){
                max = sameLetters;
                distance = i;
        }
    }
    return distance;
}

char *read_Input_Msg(int *msglen)
{//input messages, at the same time counts the length of the entered string
    int capacity = INT_MSG_LEN;
    char *msg = malloc(capacity);
    int c, len = 0;
    while ((c = getchar()) != EOF && c != '\n'){
        if (!((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z'))) {
            free(msg);
            msg = NULL;
            len = 0;
            break;
        }
        if (len == capacity){
            char *tmp = realloc(msg, capacity * 2);
            if (tmp == NULL){
                free(msg);
                msg = NULL;
                len = 0;
                break;
            }
            capacity *= 2;
            msg = tmp;
        }
        msg[len++] = c;
    }
    *msglen = len;
    return msg;
}

Solution

You fail because you call shift with msgres == null

msgEnc = msg = msgRes = mainMsg = NULL; <<<<==========
msgEncLen = msgLen = 0;

msgEnc = read_Input_Msg(&msgEncLen);
if (msgEnc)
    msg = read_Input_Msg(&msgLen);

if (msgEnc == NULL || msg == NULL)
    ret = ERROR_INPUT;
else if (msgEncLen != msgLen)
    ret = ERROR_LEN;

if (ret == NO_ERROR)
    shift(msgEnc, msg, msgRes, mainMsg, alphabet, msgEncLen);  <<<<======

Answered By - pm100

Answer Checked By - Candace Johnson (PHPFixing Volunteer)