如何识别和解决 C 中的分段错误错误？

Question

编译并运行“project1.exe”后，我使用调试器收到了一个 SIGSEGV 错误，并且无法发现导致问题的原因。 调试器将问题追溯到“combine_like_terms”方法，但我不确定是什么原因造成的。 对于项目的任何部分，我们将不胜感激。 我正在使用 cygwin 编译和运行程序。

对于背景，我只能编辑 printandcombine.c 和 printandcombine.h 文件：

printandcombine.h：

#ifndef PRINTANDCOMBINE_H
#define PRINTANDCOMBINE_H

//Returns a string representation of the struct term_t
char * term_to_string(term_t * term);

//Prints a linkedlist in no specific order
void print_linklist(node_t * curr);

//Returns a new linkedlist that is the result of combining the like terms
node_t * combine_like_terms(const node_t * current_node_ptr);

#endif

printandcombine.c：

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

/* Functions */

char * term_to_string(term_t * term)
{
    char *str = malloc((sizeof(char)) * 1024);
    
    sprintf(str, "%d%c%d ", term->coefficient, term->var,   term->exponent);
    printf("%s", str);

    free(str);

    return str;
}

void print_linklist(node_t * curr)
{
    printf("%s", term_to_string(curr->term));

    if (!(curr->next_node == NULL))
    {
        print_linklist(curr->next_node);
    }
}

node_t * combine_like_terms(const node_t * current_node_ptr)
{
    node_t *temp = (node_t *)current_node_ptr;

    node_t *out = malloc(sizeof(node_t));
    node_t *move = out;

    int x = 0;

    while (!(temp == NULL))
    {
        if (temp->term->exponent > x)
        {
            x =temp->term->exponent;
        }
        temp = temp->next_node;
    }
    
    for (; x >= 0; x--)
    {
        temp = (node_t *)current_node_ptr;
        int a = 0;
        while (!(temp == NULL))
        {
            if (temp->term->exponent == x)
            {
                a = a + temp->term->coefficient;
            }
        
        move->term->coefficient = a;
        move->term->var = 'x';
        move->term->exponent = x;
        if (x > 0)
        {
        move->next_node = (node_t *)malloc(sizeof(node_t));
        move = move->next_node;
        }
    }
            
}

return out;
}

项目1.c：

/* This is your main file */
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include"common.h"
#include"buildlinklist.h"
#include"printandcombine.h"

int main() {
    node_t * node_ptr = NULL;
    node_t * new_node_ptr=NULL;

    printf("NAME: Name\n");
    
    /* Build linklist */
    read_objects(&node_ptr);

    
    /* Print the link list */
    printf("Original: ");
    print_linklist(node_ptr);
    
    /* Combine like terms in the link list and create a new link list */
    new_node_ptr=combine_like_terms(node_ptr);
    printf("\nCombined: : ");
    /* Print new combine linklist */
    print_linklist(new_node_ptr);

    printf("\nNAME: Name\n");
    free(node_ptr);
    free(new_node_ptr);
    return 0;


}

构建列表.h：

#ifndef BUILDLINKLIST_H
#define BUILDLINKLIST_H

#include"common.h"


/* Read from a text file and put in to a term_t structure. Then create a linklist of node (each node has an element of term struct.)*/
void read_objects(node_t ** pointer_to_node_ptr);

/* Assign value to term_t object elements */
term_t * term_from_string(char * buff);

/* Add a node to the link list */
int add_node(node_t ** pointer_to_node_ptr, void * term);

#endif

buildlist.c：

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



/* Assign value to term_t object elements */
term_t * term_from_string(char * buff) {
    term_t * ret = malloc(sizeof(term_t));
    ret->coefficient=atoi(strtok(buff, " "));
    ret->var=*strtok(NULL, " ");
    ret->exponent=atoi(strtok(NULL, " "));
    return ret;
}


/* Add a node to the link list */
int add_node(node_t ** pointer_to_node_ptr, void * term) {
  int ret = 0;
  node_t * newnode_ptr = (node_t *) malloc(sizeof(node_t));
  if (newnode_ptr == NULL) {
    ret = -1;
  }
  else {
    newnode_ptr->term = term;
    newnode_ptr->next_node = *pointer_to_node_ptr;
    *pointer_to_node_ptr = newnode_ptr;
  }
  return ret;
}


/* Read from a text file and put in to a term_t structure. Then create a linklist of node (each node has an element of term struct.)*/
void read_objects(node_t ** pointer_to_node_ptr) {

    FILE *fp;
    char buffer[BUFFERLEN];
    fp = fopen("terms.txt", "r");

    while (fgets(buffer, BUFFERLEN,fp)) {
        term_t * this_term;
        this_term =  term_from_string(buffer);
        add_node(pointer_to_node_ptr, this_term);
    }
    fclose(fp);
}

常见的.h：

#ifndef COMMON_H
#define COMMON_H

#define BUFFERLEN 40

typedef struct{           /* struct to hold elements like: 3x4 */
    int coefficient;
    char var;
    int exponent;
} term_t;

typedef struct node {
  term_t * term;            /* pointer to term */
  struct node * next_node;  /* pointer to next node */
} node_t;

#endif

makefile：

CC=gcc 
CFLAGS=-std=c11 -Wall -pedantic 

all: project1.c buildlinklist.o printandcombine.o
    $(CC) $(CFLAGS) project1.c buildlinklist.o printandcombine.o -o project1

buildlinklist.o: buildlinklist.c
    $(CC) $(CFLAGS) -c buildlinklist.c

printandcombine.o: printandcombine.c
    $(CC) $(CFLAGS) -c printandcombine.c
clean:
    rm -f *.o *~ project1.exe