每次我运行我的程序时，strtok() 的输出都会给出不同的行为

【问题标题】：Output of strtok() gives different behaviour every time I run my program每次我运行我的程序时，strtok() 的输出都会给出不同的行为
【发布时间】：2015-10-25 20:09:25
【问题描述】：

我的 C89 编程任务的一部分涉及将文本文件的内容读取到链接列表中，该文本文件在一行中包含未知数量的单词。单词由空格分隔。我想，输入 strtok。

我的函数尚未 100% 完成，但它能够正确地从缓冲区中抓取单词（之前使用 fgetc 逐字符读取）并将它们粘贴到链表节点的“单词”字段中，并且我只是在检查是否可以在继续之前再次打印这些单词。

例如如果：here are some words in the user file\0 是缓冲区的内容，则输出如下所示：

head->word = here
head->word = are
head->word = some
head->word = words
...

正如预期的那样。但是，有时在运行时输出有点奇怪，通常表现为单词从开头或结尾或两者都缺少一个或两个字符。有时似乎一个单词被切成两半，其中的一部分跨越两行输出。这是来自同一个可执行文件！在过去的一个小时里，我阅读了其他几个主题，一无所获，完全被难住了——我想我最好先解决这个问题，然后再继续，以防我的整个方法需要改变。

我的代码在下面，对于这个令人沮丧的事情，任何帮助都表示赞赏......是时候获取另一个 Red Bull methinks。

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

#include "nodestruct.h"

char** readUserfile(char** userFilename, int* numUserwords)
{
    /* Open user file for reading */
    FILE* userPtr = fopen(*userFilename, "r");

    char ch = (char)fgetc(userPtr); /* 'ch' temporarily stores input taken by fgetc() */

    int length = 0; /* Eventually the length of the file's line, +1 for a null terminator */

    char **userArray = NULL;

    /* Creating a temporary buffer to store the contents of the user file. The buffer is allowed to grow
    until it holds the contents of the file, as we are told the user file has all it's words on one line,
    separated by whitespace, however we do not know the total number of words preventing us from using
    fgets() to read in the line (unless we make an arbitrary decision on a very big 'size' argument) */
    int BUFFER_SIZE = 128;
    char* buffer = (char*)malloc( sizeof(char) * BUFFER_SIZE );

    /* Delimiter for call to strtok() below: the whitespace that separates words in the user file */
    char delim = ' ';
    const char* delimPtr = &delim;
    /* String to catch return value of strtok() so we can check if non-null (i.e. returns a word) or null
    (end the linked list at this word) */
    char* strtokReturn;

    /* Read user file: */
    /* While still contents to be read */
    while(ch != EOF)
    {
        if(length != BUFFER_SIZE)
        {
            buffer[length] = ch;
            length++;
        }
        else    /* Buffer is full, so realloc, doubling the size each time */
        {
            BUFFER_SIZE *= 2;
            buffer = realloc(buffer, BUFFER_SIZE);
            buffer[length] = ch;
            length++;
        }
        /* Read the next character. If EOF reached, the while loop condition will stop the read */
        ch = (char)fgetc(userPtr);
    }

    /* Trim the buffer to only contain the information that was read + '\0' */
    buffer = realloc(buffer, (sizeof(char) * (length+1)) );
    buffer[length] = '\0';

    /* Just a note in case the user file was empty */
    if(length == 0)
    {
        printf("Note: no words found in user file.\n");
    }

    /* Create a linked list containing all the words read by the above method */
    Node* head = (Node*)malloc(sizeof(Node));

    /* Enter the first word into the list - strtok() is used here to begin breaking up the contents of the
    buffer read previously into separate strings (words). The delimiter is the whitespace character ' ' */

    strtokReturn = strtok(buffer, delimPtr);
    strcpy(head->word, strtokReturn); 
    printf("head->word = <<%s>>\n", head->word);
    head->next = NULL;

    strtokReturn = strtok(NULL, delimPtr);
    strcpy(head->word, strtokReturn); 
    printf("head->word = <<%s>>\n", head->word);
    head->next = NULL;

    strtokReturn = strtok(NULL, delimPtr);
    strcpy(head->word, strtokReturn); 
    printf("head->word = <<%s>>\n", head->word);
    head->next = NULL;

    strtokReturn = strtok(NULL, delimPtr);
    strcpy(head->word, strtokReturn); 
    printf("head->word = <<%s>>\n", head->word);
    head->next = NULL;

    strtokReturn = strtok(NULL, delimPtr);
    strcpy(head->word, strtokReturn); 
    printf("head->word = <<%s>>\n", head->word);
    head->next = NULL;

    strtokReturn = strtok(NULL, delimPtr);
    strcpy(head->word, strtokReturn); 
    printf("head->word = <<%s>>\n", head->word);
    head->next = NULL;

    strtokReturn = strtok(NULL, delimPtr);
    strcpy(head->word, strtokReturn); 
    printf("head->word = <<%s>>\n", head->word);
    head->next = NULL;

    strtokReturn = strtok(NULL, delimPtr);
    strcpy(head->word, strtokReturn); 
    printf("head->word = <<%s>>\n", head->word);
    head->next = NULL;

    strtokReturn = strtok(NULL, delimPtr);
    strcpy(head->word, strtokReturn); 
    printf("head->word = <<%s>>\n", head->word);
    head->next = NULL;

    strtokReturn = strtok(NULL, delimPtr);
    strcpy(head->word, strtokReturn); 
    printf("head->word = <<%s>>\n", head->word);
    head->next = NULL;

    strtokReturn = strtok(NULL, delimPtr);
    strcpy(head->word, strtokReturn); 
    printf("head->word = <<%s>>\n", head->word);
    head->next = NULL;



    free(head);
    head = NULL;

    free(buffer);
    buffer = NULL;

    fclose(userPtr);
    return userArray;
}/* End readUserfile() */

输出（请原谅长度，但为了充分披露）：

[Danyal@DanCentos assign]$ ./wordfixr userfile.txt
Spellrc opened/read successfully.
Dictionary file opened successfully.
Dictionary read successfully.
head->word = <<here>>
head->word = <<are>>
head->word = <<some>>
head->word = <<words>>
head->word = <<in>>
head->word = <<the>>
head->word = <<user>>
head->word = <<file>>
head->word = <<and>>
head->word = <<the>>
head->word = <<whole>>
[Danyal@DanCentos assign]$ ./wordfixr userfile.txt
Spellrc opened/read successfully.
Dictionary file opened successfully.
Dictionary read successfully.
head->word = <<h>>
head->word = <<r>>
head->word = <<ar>>
head->word = <<som>>
head->word = <<words>>
head->word = <<in>>
head->word = <<th>>
head->word = <<us>>
head->word = <<r>>
head->word = <<fil>>
head->word = <<and>>
[Danyal@DanCentos assign]$ ./wordfixr userfile.txt
Spellrc opened/read successfully.
Dictionary file opened successfully.
Dictionary read successfully.
head->word = <<here>>
head->word = <<are>>
head->word = <<some>>
head->word = <<words>>
head->word = <<in>>
head->word = <<the>>
head->word = <<user>>
head->word = <<file>>
head->word = <<and>>
head->word = <<the>>
head->word = <<whole>>
[Danyal@DanCentos assign]$ ./wordfixr userfile.txt
Spellrc opened/read successfully.
Dictionary file opened successfully.
Dictionary read successfully.
head->word = <<here>>
head->word = <<are>>
head->word = <<some>>
head->word = <<words>>
head->word = <<in>>
head->word = <<the>>
head->word = <<user>>
head->word = <<file>>
head->word = <<and>>
head->word = <<the>>
head->word = <<whole>>
[Danyal@DanCentos assign]$ ./wordfixr userfile.txt
Spellrc opened/read successfully.
Dictionary file opened successfully.
Dictionary read successfully.
head->word = <<here>>
head->word = <<are>>
head->word = <<some>>
head->word = <<words>>
head->word = <<in>>
head->word = <<the>>
head->word = <<user>>
head->word = <<file>>
head->word = <<and>>
head->word = <<the>>
head->word = <<whole>>
[Danyal@DanCentos assign]$ ./wordfixr userfile.txt
Spellrc opened/read successfully.
Dictionary file opened successfully.
Dictionary read successfully.
head->word = <<here>>
head->word = <<are>>
head->word = <<some>>
head->word = <<words>>
head->word = <<in>>
head->word = <<the>>
head->word = <<user>>
head->word = <<file>>
head->word = <<and>>
head->word = <<the>>
head->word = <<whole>>
[Danyal@DanCentos assign]$ ./wordfixr userfile.txt
Spellrc opened/read successfully.
Dictionary file opened successfully.
Dictionary read successfully.
head->word = <<here>>
head->word = <<are>>
head->word = <<some>>
head->word = <<words>>
head->word = <<in>>
head->word = <<the>>
head->word = <<user>>
head->word = <<file>>
head->word = <<and>>
head->word = <<the>>
head->word = <<whole>>
[Danyal@DanCentos assign]$ ./wordfixr userfile.txt
Spellrc opened/read successfully.
Dictionary file opened successfully.
Dictionary read successfully.
head->word = <<h>>
head->word = <<r>>
head->word = <<ar>>
head->word = <<som>>
head->word = <<words>>
head->word = <<in>>
head->word = <<th>>
head->word = <<us>>
head->word = <<r>>
head->word = <<fil>>
head->word = <<and>>
[Danyal@DanCentos assign]$ ./wordfixr userfile.txt
Spellrc opened/read successfully.
Dictionary file opened successfully.
Dictionary read successfully.
head->word = <<here>>
head->word = <<are>>
head->word = <<some>>
head->word = <<words>>
head->word = <<in>>
head->word = <<the>>
head->word = <<user>>
head->word = <<file>>
head->word = <<and>>
head->word = <<the>>
head->word = <<whole>>
[Danyal@DanCentos assign]$ ./wordfixr userfile.txt
Spellrc opened/read successfully.
Dictionary file opened successfully.
Dictionary read successfully.
head->word = <<here>>
head->word = <<are>>
head->word = <<some>>
head->word = <<words>>
head->word = <<in>>
head->word = <<the>>
head->word = <<user>>
head->word = <<file>>
head->word = <<and>>
head->word = <<the>>
head->word = <<whole>>
[Danyal@DanCentos assign]$ ./wordfixr userfile.txt
Spellrc opened/read successfully.
Dictionary file opened successfully.
Dictionary read successfully.
head->word = <<here>>
head->word = <<are>>
head->word = <<some>>
head->word = <<words>>
head->word = <<in>>
head->word = <<the>>
head->word = <<user>>
head->word = <<file>>
head->word = <<and>>
head->word = <<the>>
head->word = <<whole>>
[Danyal@DanCentos assign]$ ./wordfixr userfile.txt
Spellrc opened/read successfully.
Dictionary file opened successfully.
Dictionary read successfully.
head->word = <<here>>
head->word = <<are>>
head->word = <<some>>
head->word = <<words>>
head->word = <<in>>
head->word = <<the>>
head->word = <<user>>
head->word = <<file>>
head->word = <<and>>
head->word = <<the>>
head->word = <<whole>>
[Danyal@DanCentos assign]$ ./wordfixr userfile.txt
Spellrc opened/read successfully.
Dictionary file opened successfully.
Dictionary read successfully.
head->word = <<here>>
head->word = <<are>>
head->word = <<some>>
head->word = <<words>>
head->word = <<in>>
head->word = <<the>>
head->word = <<user>>
head->word = <<file>>
head->word = <<and>>
head->word = <<the>>
head->word = <<whole>>
[Danyal@DanCentos assign]$ ./wordfixr userfile.txt
Spellrc opened/read successfully.
Dictionary file opened successfully.
Dictionary read successfully.
head->word = <<here>>
head->word = <<are>>
head->word = <<some>>
head->word = <<wor>>
head->word = <<s>>
head->word = <<in>>
head->word = <<the>>
head->word = <<user>>
head->word = <<file>>
head->word = <<an>>
head->word = <<the>>

请注意，我更改了 printf 语句以将打印的字符串封装在一些括号中，以确保没有在另一个线程中看到的不可见字符，但正如您所看到的那样，只打印了单词。

再次感谢您的任何帮助，我真的很感激，并且真的很感激生活在一个免费存在堆栈溢出之类的地方的时代。

【问题讨论】：

  • Node的定义在哪里？你在为head-&gt;word分配内存吗？
  • 是的，对不起，节点的声明在“nodestruct.h”头文件中：#define MAX_STRING_LEN 51 typedef struct Node { char word[MAX_STRING_LEN]; struct Node* next; }Node*

标签： c linked-list strtok


【解决方案1】：

strtok 的第二个参数应该是一个以 null 结尾的字符串。 strtok 认为该字符串的任何元素都是有效的分隔符。如果您只想要一个分隔符，请使用长度为 1 的字符串：

strtokReturn = strtok(buffer, " ");

没有'\0' 来终止您的delimPtr，strtok 正在查看恰好跟随delim 的字节。显然，它有时会在 '\0' 字符之前找到一个 'e' 字符，并最终将 'e' 视为另一个分隔符。

【讨论】：

  • 您说的很有道理，我更改了函数以反映这一点：char delim[] = " \0"; const char* delimPtr = delim; 但是，当我这次运行程序时，似乎产生了相同的结果。我应该注意，一个 int 指针的值告诉我我的链接列表从 20（一个太长）更改为 19 的时间，这应该是（原始文本文件中的字数）。跨度>
  • 奇怪...我注意到 valgrind 没有报告内存泄漏的错误，这很奇怪，因为我还没有正确释放我新创建的链表。当我未完成的函数只有一个“头”节点时，我最后有一个 free(head) 来释放它，但现在我已经确认有一个包含 19 个节点的链表，我只留下了一个 free(head) 没有释放整个列表，我很惊讶 valgrind 没有告诉我我丢失了那么多块......
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