每次运行程序时，strtok（）的输出都会产生不同的行为

时间：2015-10-25 20:09:25

标签： c linked-list strtok

我的C89编程任务的一部分涉及将文本文件的内容（包含一行中未知数量的单词）读入链接列表。单词由空格分隔。我想，输入strtok。

我的功能还没有100％完成，但它能够正确地从缓冲区中获取单词（之前用fgetc逐个字符地读取）并将它们粘贴在链表节点的“word”字段中，并且我只是在检查是否可以在继续之前再打印出来。

E.g。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
...

这是预期的。但是，有时在运行输出时有点奇怪，通常表现为从开头或结尾或两者都缺少一个或两个字符的单词。有时，似乎一个单词被切成两半，其中一部分跨越两行输出。这是来自同一个可执行文件！在过去的几个小时里，我已经阅读了其他一些线索，并且完全被困住了 - 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，任何帮助都会在这个令人沮丧的事情上受到赞赏......是时候再拿一个红牛了。

#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（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>>

就在n.b.，我更改了printf语句，将打印的字符串封装在一些括号中，以确保没有其他线程中看到的不可见字符，但正如您所看到的那样，只打印了该字。

再次感谢您的任何帮助，我真的很感激，我真的很感激生活在一个像堆栈溢出的地方免费存在的时候。

1 个答案:

答案 0 :(得分：0)

strtok的第二个参数应该是以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，则strtok会查看恰好跟随delim的字节。显然，它有时会在'e'字符之前找到'\0'个字符，并最终将'e'视为另一个分隔符。

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