求助，段错误怎么办

[lybcyd]

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

int len = 0;

struct node
{  
  char *word;
  int count;
  struct node *next;   
}*head,*p,*q;

struct node* printf_sort(struct node *head)
{
  struct node *p1,*p2,*ptemp,*pfinished = NULL;
for (p1 = head; p1->next != pfinished;)
{
  for (p2 = p1; p2->next != pfinished;)
{
if (p2->count < p2->next->count)
  {
if (p2 == p1)
{
p1 = p2->next;
p2->next = p1->next;
p1->next = p2;
ptemp = p1;
}
else
{
ptemp->next = p2->next;
ptemp = p2->next;
p2->next = ptemp->next;
ptemp->next = p2;
}
}
else
{
ptemp = p2;
p2=p2->next;
}
}
pfinished = p2;
}
}
int main(int argc, char *argv[])
{
  int ndisp = 0;
  struct timeval starttime, endtime, durtime;
  int i = 0;

  /* step0: get cmd parameter and check it */

  if (argc < 2){
  printf("USAGE: wordcount <filename> [Top # of results to display]\n");
  exit(0);
  }
  char *filename = *(argv + 1);
    
  /* step1: prepare work (e.g. open file, load file to memory ...) */
    
  FILE *file;
  if ((file = fopen(filename, "r")) == NULL){
  printf("cannot open this file\n");
  exit(0);
  }
  printf("wordcount: Running...\n");
  gettimeofday(&starttime, 0);

  /* step2: do word count */

  char ch;
  head = NULL;
  while ((ch = fgetc(file)) != EOF)
  {
  while (ch == ' ')
  ch = fgetc(file);
  if (ch <= 'Z')
  ch += 32;
  i = 0;
  q = (struct node *) malloc(sizeof(struct node));
  char temp[20];  
  while (ch = fgetc(file) != ' ')   
  {
  temp[i] = ch;
  i++;
  }
  int same = 0;
  for (p = head; p != NULL; p = p->next)
  {
  if (strcmp(temp, p->word) == 0)
  {
  p->count++;
  same = 1;
  }
  }
  if (same == 0)
  {
  strcpy(q->word, temp);
  p->next = q;
  }
  }
  gettimeofday(&endtime, 0);
  GET_TIME(starttime, endtime, durtime);
  printf("wordcount: completed %ld.%ld(s)\n", durtime.tv_sec, durtime.tv_usec);


  printf("wordsort: running ...\n");
  gettimeofday(&starttime, 0);	

  /* step3: sort the results */

  printf_sort(head);
  gettimeofday(&endtime, 0);
  GET_TIME(starttime, endtime, durtime);
  printf("wordsort: completed %ld.%ld(s)\n", durtime.tv_sec, durtime.tv_usec);


  /* step4: print results */
  ndisp = head->count;
  printf("\nwordcount: results (TOP %d from %d):\n", ndisp, len);
  p = head;
  if (head != NULL)
  {
  do
  {
  printf("%s - %d\n", p->word, p->count);
  p = p->next;
  }while (p != NULL);
  }
  /* step5: destroy work (e.g. free memory, close file ...) */
  fclose(file);
  free(head);
  return 0;
}

如上。程序目的是读入文件的单词并统计每一个单词的数目，然后按照数目降序打印出来。
编译可以通过，运行发生段错误，调试发现如下错误：
0x00007ffff7b664e2 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
希望各位帮忙解决一下

[jemofh159]

free(head) 这里错了没？你自己慢慢调吧 眼睛有点花

[AnYidan]

段错误一般是非法使用了内存，越界或非法解指针

[cikerexue]

慢慢调试吧，设断点一步一步看，看卡在哪里

[cikerexue]

慢慢调试吧，设断点一步一步看，看卡在哪里

[pengfoo]

段错误肯定是指针的引用不当造成的

[lybcyd]

能不能帮忙指出错误之处？谢谢了！[Quote=引用 1 楼 的回复:]

段错误肯定是指针的引用不当造成的
[/Quote]

[ice_wind1213]

看了一遍 ，蒙了，坐等高手~

[youngyang]

while (ch = fgetc(file) != ' ') 这错了 ch永远是0或者1
{
temp[i] = ch;
i++;
}
眼睛有点花 你再找找吧。

[jemofh159]

LS不对吧，fgetc返回的是读到的一个字节。

[wzhwisk]

错误的指针引用，仔细找吧，这种东西非要自己试验才有收获的

[youngyang]

[Quote=引用 5 楼 的回复:]

LS不对吧，fgetc返回的是读到的一个字节。
[/Quote]
while (ch = fgetc(file) != ' ') 等价于while (ch = (fgetc(file) != ' '))
ch不为0或者1 能是什么

搂主用ch = fgetc(file)来接收也是不对的
ch是char类型 fgetc函数返回int类型 被截为char型
正常的字符可能会被错误的解释为EOF，或者EOF可能会被修改