快速排序抛出分段错误

Question

我必须写一个快速排序，得到一个txt，它有最通用的密码和频率。

我还有一个必须正确的文件 ma​​in.c。我只需要编写快速排序的函数。

当我查看代码时，似乎一切正常。我也用了valgrind，但是找不到错误。

看一下，代码末尾是valgrind的结果。

#define _POSIX_C_SOURCE 200809L
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include "quicksort.h"

void init_list(list *mylist) {
    mylist = (list*)malloc(sizeof(list));
    mylist->first = NULL;
    mylist->last = NULL;
}

void insert_list(list_element *le, list *mylist) {
    le->next = NULL;

    if (mylist->first == NULL) {
        mylist->first = le;
        mylist->first->next = NULL;

        if (mylist->last == NULL) {
            mylist->last = le;
        }
    } else
    if (mylist->first != NULL) {
        if (mylist->first->next == NULL) {
            mylist->first->next = le;
            mylist->last = le;
    } else
    if (mylist->first->next != NULL) {
            list_element *h = mylist->first->next;
            list_element *hc = NULL;
            while (h != NULL) {
                hc = h;
                h = h->next;
            }
            hc->next = le;
            mylist->last = le;
        }
    }
}

void free_list(list *mylist) {
    list_element *zaehler;
    list_element *zaehler2 = NULL;

    for (zaehler = mylist->first; zaehler != mylist->last; zaehler = zaehler2) {
        zaehler2 = zaehler->next;
        free(zaehler);
    }
    free(mylist);
}

void read_data(char *filename, list *mylist) {
    FILE *input = fopen(filename, "r");
    if (input == NULL) {
        printf("Could not open file\n");
        return;
    }
    char *zeile = malloc(50 * sizeof(char));
    char *leer = " ";
    while (fgets(zeile, 50, input) != NULL) {
        char *token1 = strtok(zeile, leer);
        char *token2 = strtok(NULL, "\n");
        list_element *new;
        new = (list_element*)malloc(sizeof(list_element));
        new->password = token1;
        new->count = atoi(token2);
        insert_list(new, mylist);
    }
}

list_element *partition(list *input, list *left, list *right) {
    list_element *pivot = input->first;
    list_element *zaehler = pivot->next;

    while (zaehler != input->last) {
        if (zaehler->count < pivot->count) {
            insert_list(zaehler, left);
        } else {
            insert_list(zaehler, right);
        }
    }
    if (zaehler == input->last) {
        if (zaehler->count < pivot->count) {
            insert_list(zaehler, left);
        } else {
            insert_list(zaehler, right);
        }
   }
    return pivot;
}

void qsort_list(list *mylist) {
    if (mylist->first == mylist->last) {
        return;
    } else {
        list *left = NULL;
        list *right = NULL;
        list_element *pivot;
        pivot = partition(mylist, left, right);
        qsort_list(left);
        qsort_list(right);
        if (left->first == NULL) {
            mylist->first = pivot;
        } else {
            mylist->first = left->first;
            left->last->next = pivot;
        }
        if (right->first == NULL) {
            pivot->next = NULL;
            mylist->last = pivot;
        } else {
            pivot->next = right->first;
            mylist->last = right->last;
        }
    }
}

void print_list(list *mylist) {
    list_element *first = mylist->first;
    list_element *last = mylist->last;
    list_element *zaehler;
    for (zaehler = first; zaehler != last; zaehler = zaehler->next) {
        printf("%s %d\n", zaehler->password, zaehler->count);
    }
    printf("%s %d\n", last->password, last->count);
}

这是 VALGRIND 所说的：

==4996== Memcheck, a memory error detector
==4996== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==4996== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==4996== Command: ./a1 Eingabedaten_quicksort_unsortiert
==4996== 
==4996== Conditional jump or move depends on uninitialised value(s)
==4996==    at 0x4007DC: insert_list (introprog_quicksort.c:34)
==4996==    by 0x4009D1: read_data (introprog_quicksort.c:90)
==4996==    by 0x400C8C: main (main_quicksort.c:13)
==4996== 
==4996== Conditional jump or move depends on uninitialised value(s)
==4996==    at 0x400824: insert_list (introprog_quicksort.c:42)
==4996==    by 0x4009D1: read_data (introprog_quicksort.c:90)
==4996==    by 0x400C8C: main (main_quicksort.c:13)
==4996== 
==4996== Use of uninitialised value of size 8
==4996==    at 0x400831: insert_list (introprog_quicksort.c:43)
==4996==    by 0x4009D1: read_data (introprog_quicksort.c:90)
==4996==    by 0x400C8C: main (main_quicksort.c:13)
==4996== 
==4996== Use of uninitialised value of size 8
==4996==    at 0x40085E: insert_list (introprog_quicksort.c:47)
==4996==    by 0x4009D1: read_data (introprog_quicksort.c:90)
==4996==    by 0x400C8C: main (main_quicksort.c:13)
==4996== 
==4996== Use of uninitialised value of size 8
==4996==    at 0x40086E: insert_list (introprog_quicksort.c:48)
==4996==    by 0x4009D1: read_data (introprog_quicksort.c:90)
==4996==    by 0x400C8C: main (main_quicksort.c:13)
==4996== 
==4996== Invalid read of size 8
==4996==    at 0x40088C: insert_list (introprog_quicksort.c:52)
==4996==    by 0x4009D1: read_data (introprog_quicksort.c:90)
==4996==    by 0x400C8C: main (main_quicksort.c:13)
==4996==  Address 0x111e2d8d48550030 is not stack'd, malloc'd or (recently) free'd
==4996== 
==4996== 
==4996== Process terminating with default action of signal 11 (SIGSEGV)
==4996==  General Protection Fault
==4996==    at 0x40088C: insert_list (introprog_quicksort.c:52)
==4996==    by 0x4009D1: read_data (introprog_quicksort.c:90)
==4996==    by 0x400C8C: main (main_quicksort.c:13)
==4996== 
==4996== HEAP SUMMARY:
==4996==     in use at exit: 642 bytes in 4 blocks
==4996==   total heap usage: 5 allocs, 1 frees, 4,738 bytes allocated
==4996== 
==4996== 16 bytes in 1 blocks are definitely lost in loss record 1 of 4
==4996==    at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4996==    by 0x40079B: init_list (introprog_quicksort.c:24)
==4996==    by 0x400C72: main (main_quicksort.c:12)
==4996== 
==4996== LEAK SUMMARY:
==4996==    definitely lost: 16 bytes in 1 blocks
==4996==    indirectly lost: 0 bytes in 0 blocks
==4996==      possibly lost: 0 bytes in 0 blocks
==4996==    still reachable: 626 bytes in 3 blocks
==4996==         suppressed: 0 bytes in 0 blocks
==4996== Reachable blocks (those to which a pointer was found) are not shown.
==4996== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==4996== 
==4996== For counts of detected and suppressed errors, rerun with: -v
==4996== Use --track-origins=yes to see where uninitialised values come from
==4996== ERROR SUMMARY: 7 errors from 7 contexts (suppressed: 0 from 0)
Segmentation fault

Answer 1

将来，询问有关您不理解的错误消息的问题可能会有所帮助。尝试类似“什么是......是什么意思？”或“我如何破译……？”。

==4996== Conditional jump or move depends on uninitialised value(s)
==4996==    at 0x4007DC: insert_list (introprog_quicksort.c:34)

这告诉你在第 34 行使用了一个未初始化的值。让我们看看第 34 行：

if ( mylist->first == NULL ) { //c.34

所以mylist 或mylist->first 未初始化。让我们深入研究您粘贴的跟踪，到第 90 行，如下一行所示：==4996== by 0x4009D1: read_data (introprog_quicksort.c:90)

new = (list_element*)malloc(sizeof(list_element));
new->password = token1;
new->count = atoi(token2);
insert_list(new, mylist); //c.90

啊！我懂了！ mylist->first 未初始化，因为它尚未被分配！巧合多吗？我想不是。这很有意义。

现在您已经了解了这些错误消息的简要说明，您应该能够完成其余部分并清除它们......您的段错误可能是由这些错误引起的。

另见BLUEPIXY留下的cmets；它们是值得考虑的有用点。