c - 每次运行程序时 strtok() 的输出都会给出不同的行为

Question

我的 C89 编程任务的一部分涉及将文本文件的内容(一行中包含未知数量的单词)读取到链接列表中。单词之间用空格分隔。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 逐个字符读取)并将它们粘贴到链表节点的“单词”字段中，并且我只是在继续之前检查是否可以再次打印出这些文字。

例如如果:这里是用户文件中的一些单词\0是缓冲区的内容，那么输出如下所示:

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

这符合预期。然而，有时运行时的输出有点奇怪，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，其中一部分跨两行输出。这是来自同一个可执行文件!在过去的一个小时里，我读了其他几篇文章，但一无所获，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。

我的代码如下，对于这个令人沮丧的事情，任何帮助都会受到赞赏......我想是时候去拿另一个红牛了。

#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，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，仅打印了单词。

再次提前感谢您的帮助，我真的很感激，并且非常感激生活在像堆栈溢出这样的地方免费存在的时代。

Answer 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。如果您只需要一个分隔符，请使用长度为 1 的字符串:

strtokReturn = strtok(buffer, " ");

如果没有 '\0' 来终止 delimPtr，strtok 就会查看紧随 delim< 的字节。显然，它有时会在 '\0' 字符之前找到 'e' 字符，并最终将 'e' 视为另一个分隔符。