Question

我遇到了seg.faults的问题。该程序运行良好，但对于很少的未知字符串，它会导致分段错误。我用Valgrind运行程序，它报告“无效的读/写大小1”，大多数问题与strcpy和strlen有关。

==5623== ERROR SUMMARY: 12 errors from 4 contexts (suppressed: 2 from 2)
==5623== 
==5623== 1 errors in context 1 of 4:
==5623== Invalid write of size 1
==5623==    at 0x4C2D812: strcpy (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5623==    by 0x400955: sameWords (main.c:62)
==5623==    by 0x400A6F: main (main.c:85)
==5623==  Address 0x51fd093 is 0 bytes after a block of size 3 alloc'd
==5623==    at 0x4C2CD7B: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5623==    by 0x40092B: sameWords (main.c:59)
==5623==    by 0x400A6F: main (main.c:85)
==5623== 
==5623== 
==5623== 1 errors in context 2 of 4:
==5623== Invalid write of size 1
==5623==    at 0x4C2D812: strcpy (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5623==    by 0x400942: sameWords (main.c:61)
==5623==    by 0x400A6F: main (main.c:85)
==5623==  Address 0x51fd045 is 0 bytes after a block of size 5 alloc'd
==5623==    at 0x4C2CD7B: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5623==    by 0x400913: sameWords (main.c:58)
==5623==    by 0x400A6F: main (main.c:85)
==5623== 
==5623== 
==5623== 4 errors in context 3 of 4:
==5623== Invalid read of size 1
==5623==    at 0x4C2D7B4: strlen (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5623==    by 0x4009EC: sameWords (main.c:70)
==5623==    by 0x400A6F: main (main.c:85)
==5623==  Address 0x51fd093 is 0 bytes after a block of size 3 alloc'd
==5623==    at 0x4C2CD7B: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5623==    by 0x40092B: sameWords (main.c:59)
==5623==    by 0x400A6F: main (main.c:85)
==5623== 
==5623== 
==5623== 6 errors in context 4 of 4:
==5623== Invalid read of size 1
==5623==    at 0x4C2D7B4: strlen (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5623==    by 0x40099E: sameWords (main.c:65)
==5623==    by 0x400A6F: main (main.c:85)
==5623==  Address 0x51fd045 is 0 bytes after a block of size 5 alloc'd
==5623==    at 0x4C2CD7B: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5623==    by 0x400913: sameWords (main.c:58)
==5623==    by 0x400A6F: main (main.c:85)
==5623== 
--5623-- 
--5623-- used_suppression:      2 dl-hack3-cond-1
==5623== 
==5623== ERROR SUMMARY: 12 errors from 4 contexts (suppressed: 2 from 2)

程序应该找出2个字符串是否由相同的单词组成（并忽略不同大小的字母）。我很遗憾我的代码的出现，我对编程很新，并且仍然试图学习如何编写它是可以理解的，所以我将简要解释正在做什么（至少我是这么认为）。 WordInString函数从一个字符串中取一个接一个的字，然后在另一个字符串中找到它。这个词是在动态分配的数组中复制的，因为我不知道这些单词可能有多长。然后在函数sameWords中我复制新数组中的字符串，所以我可以将所有单词转换为低位字母，然后我调用函数WordInString来搜索字符串中的单词。我的主要功能我只用2个字符串调用sameWords
代码看起来像这样。再次抱歉这个糟糕的安排。

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


int WordInString(const char *a, const char *b)
{
    /* Selecting words one after another and finding the word in another strin.
    Dynamic allocation of word string, because words lengths are unknown.*/
    char * word=NULL;
    int previous = 0;
    int length=0;
    int wordlength=0;
    int i;

    if((strlen(a)==0) && (strlen(b)==0))
        {
        return 1;
        }

    i=0;
    while(1)
        {
        if (i>=wordlength) {wordlength+=250; word=(char*) malloc(wordlength*sizeof(char));}
        if(isalpha(a[i]))
            {
            if(!isalpha(previous))
                {
                length=0;
                }
            if(length<80) word[length++] = tolower(a[i]);
            }
            else
                {
                if(length>0)
                    {
                    word[length] = '\0';
                    if(strstr(b, word)==NULL)
                        {
                        return 0;
                        }
                    length=0;
                    }
                }
                if(a[i] == '\0') {break;}
                previous=tolower(a[i++]);
        }
    free(word);
    return 1;
}

int sameWords( const char * a, const char * b)
{
    int i=0, j=0;
    char * array1=(char*) malloc(strlen(a)*sizeof(char));
    char * array2=(char*) malloc(strlen(b)*sizeof(char));
    /* copy a and b strings to new string, that are not cons, so they can be changed      tolower */
    strcpy(array1, a);
    strcpy(array2, b);

    /* convert strings to lower letters  */
    for(i=0; i<strlen(array1); i++)
        {
        array1[i]=tolower(array1[i]);
        }
    for(j=0; j<strlen(array2); j++)
        {
        array2[j]=tolower(array2[j]);
        }
    /* calling WordInString to compare */
    if (WordInString(a, array2)==0) {return 0;}
    if (WordInString(b, array1)==0) {return 0;}
    free(array1);
    free(array2);
    return 1;
}


int main ( int argc, char * argv [] )
{
    int res;
    res=(sameWords("This is a string", "This string is a string"));
    return 0;
}

我非常感谢你的帮助。我试着查一查，但无法理解。

Answer 1

malloc(strlen(a)*sizeof(char));大小+1需要字符串结尾＆＃39; \ 0＆＃39; - BLUEPIXY

C - Valgrind“strcpy / strlen时读取/写入大小为1的错误”

1 个答案: