如何修复分段错误：11编译器错误

Question

I have been learning from the C Programming Language book (K&R) and was writing one of the exercises that removes trailing blanks from an input. I understand that a segmentation fault is at some level a problem having to do with accessing memory that is not accessible, but I have read through this code several times and can't find the error. I would like it very much if someone could help find this error and tell me how to discover errors like this in the future.

#include <stdio.h>

#define MAXLINE 1000
#define CHAR 0 /*character definition*/
#define TRAIL 1 /*determines whether program is in a trailing blank*/

int getinput(char input[], int max);
int trailrem(char input[], char copyto[]);
int len;

int main() {
    char line[MAXLINE]; /*current line*/
    char newline[MAXLINE];
    int i, c, newreturn; /*integer counter, character holder, current line       length, and trailrem return value*/
    int len;

    while((len = getinput(line, MAXLINE)) > 0) {
        newreturn = trailrem(line, newline);

        for(i = 0; i <= newreturn; ++i)
            printf("\n%c\n", newline[i]);
    }

 }

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

    if(c == '\n') {
        input[i] = c;
        ++i;
   }

    input[i] = '\0';
    return i;
}

int trailrem(char input[], char copy[]) {
    int i, j, minusin, state, r;

    for(i = len; input[i] != EOF && i >= 0; --i) {
        if(input[i] =='\n')
            state = TRAIL;

        else if((input[i] == ' ' && state == TRAIL) ||( input[i] == '\t' && state == TRAIL))
            ++minusin;

        else if(state == TRAIL && (input[i] != ' ' || input[i] != '\t'))
            state = CHAR;

        for(j = (r = len-minusin); state == CHAR; --j){
                copy[j-2] = input[i];
        }
    }


    copy[r] = '\0';
    copy[r-1] = '\n';
    return r;

}

Answer 1

So many problems in your code. But the main problem is, you have a global len

int len; 

And a local len in the main function.

You are initializing len in main function like this:

while((len = getinput(line, MAXLINE)) > 0)

So the local len is updated. But the global len is still 0 .

You are expecting that, you will get the updated value of len in trailrem method but you don't. In trailrem() you will get len equal to 0 !

for(i = len; input[i] != EOF && i >= 0; --i)

So i is 0 too. And hence, copy[r-1] = '\\n'; will crash, because r-1 can be negative.

Other problems: (BLUEPIXY and WhozCraig mentioned in the comment).

for(i = 0; (c = getchar()) != EOF && c != '\n' && c < (max-1); ++i)

here, c < (max-1) should be i < (max-1) .

++minusin; in trailrem function where minusin is uninitialized.