How to fix 'Segmentation Fault (core dumped)' error

Question

I am just starting to learn some C so I wrote a small program to exercise on using char arrays. It takes in a string from stdin and prints it after removing trailing whitespaces and empty lines (if any of you have the second edition of 'The C programming language' it's problem 1-18). After hitting the EOF key to end input, however, the program exits with error: 'Segmentation fault (core dumped)'.

I've already compiled with Wall , Wextra , Werror and g but no errors are displayed at compile time (using gcc 9.1.1 on Fedora 30). I also ran the program through gdb and discovered that the line that causes the fault is this line:

for (; (c = input[start + i]) != '\n' || c != '\0'; ++i)

I'm pasting the whole file since it's a short program and everything could be the cause of the error.

#include <stdio.h>

#define MAX 100

int Read(char input[], int max);
void ProcessInput(char input[], char output[], int length);
int GetToEndLine(char input[], char outLine[], int startIndex);

int main(void){
    char input[MAX];
    char output[MAX];
    int length;
    printf("W: Max output is of %d chars.\n", MAX - 1);
    length = Read(input, MAX);
    ProcessInput(input, output, length);
    printf("\nCleaned input:\n---\n%s\n---\n", output);
    return 0;
}

int Read(char input[], int max){
    int i, c;
    for (i = 0; (c = getchar()) != EOF && i < max - 1; ++i)
        input[i] = c;
    input[i] = '\0';
    return i;
}

void ProcessInput(char input[], char output[], int length){
    int mainIndex = 0,
        new_mainIndex = 0,
        outputIndex = 0;
    char line[MAX];
    while ((length - mainIndex) > 0){
        new_mainIndex = GetToEndLine(input, line, mainIndex);
        if (new_mainIndex == mainIndex){
            ++mainIndex;
            continue;
        }
        for (int j = new_mainIndex - mainIndex; 
                line[j] == ' ' || line[j] == '\t' || line[j] != '\n'; --j)
            line[j] = '\0';
        for(int j = 0; line[j] != '\0'; ++j, ++outputIndex)
            output[outputIndex] = line[j];
        output[outputIndex] = '\n';
        ++outputIndex;
        mainIndex = new_mainIndex + 1;
    }
}

int GetToEndLine(char input[], char line[], int start){
    int c, 
        i = 0;
    for (; (c = input[start + i]) != '\n' || c != '\0'; ++i)
        line[i] = c;
    line[i] = c;
    return start + i;
}

The full output of a successful test run should be:

W: Max output is of 99 chars.
asdf   

asdf
Cleaned Input:
---
asdf
asdf
---

Instead of that I get:

W: Max output is of 99 chars.
asdf   

asdfSegmentation fault(core dumped)

Can somebody help me debug this program?

Answer 1

It appears that GetToEndLine() will continue looping until it runs out of memory. Did you mean to use a logical and instead of a logical or? Try for (; (c = input[start + i]) != '\\n' && c != '\\0'; ++i)

int GetToEndLine(char input[], char line[], int start) {
    int c,
        i = 0;
    for (; (c = input[start + i]) != '\n' && c != '\0'; ++i)
        line[i] = c;
    line[i] = c; // What is the purpose of this?
    return start + i;
}

That should fix your immediate segfault problem.