c - 我找不到导致间歇性崩溃的指针错误。你可以吗？

Question

这在大多数情况下都有效，但偶尔会发生崩溃。某处存在指针问题，但我还看不到它。

代码从字符串中取出单词，并构建它们的链表。单词必须包括相邻的标点符号，但不能有空格。例如，字符串:

He said, 'blah blah!' and then died.

会变成字符串

He

said,

'blah

blah!'

and

then

died.

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

unsigned longestword(char *str);

typedef struct _list{
    char *p;
    struct _list *next;
}list;


int main(void){
    char str[]="   'Well!' thought Alice to herself, 'after such a fall as this, I shall think nothing of tumbling down stairs!'";
    unsigned k, i=0, l, j, wordscout;
    list *curr, *root=NULL;

    k =longestword(str);
    puts(str);
    printf("\nlongest word in string is %u letters long.", k);

    do{
        //  skip over any leading whitespace.
        for(; str[i] && isspace(str[i]); i++);
        if(!str[i]) break;

        //  count length of word that begins with str[i].
        for(wordscout=i, l=0; str[wordscout] && !isspace(str[wordscout]); wordscout++, l++);

        //  if this is first word, malloc space to root.
        if(root==NULL){
            if((root = malloc(sizeof(list))) == NULL){
                printf("\nmalloc() failed.");
                exit(1);
            }
            curr = root;
        }

        //  if not first word, malloc space to curr->next.
        else{
            if((curr->next = malloc(sizeof(list))) == NULL){
                printf("\nmalloc() failed.");
                exit(1);
            }
            curr = curr->next;
        }

        //  malloc space in current struct for string.
        if((curr->p = malloc(1+l*sizeof(char))) == NULL){
            printf("\nmalloc() failed.");
            exit(1);
        }

        //  read first word into new space.
        j=0;
        while(!isspace(str[i])) curr->p[j++] = str[i++];
        curr->p[j] = '\0';

        //  check if word is there.
        printf("\n<<%s>>", curr->p);
    }while(str[wordscout]);
}


//  takes a null-terminated string, returns length of longest word in the string. word includes adjacent punctuation, but not whitespace.
unsigned longestword(char *str){

    //  check that word is null-terminated before carrying on.
    unsigned j,k,i,l;
    l = strlen(str);
    for(i=j=k=0; i<=l; i++){
        if(isalpha(str[i]) || ispunct(str[i])) j++;
        else if(j>k){ k=j; j=0; }
        else j=0;
    }
    return k;
}

longestword()函数可以忽略。它有效，稍后用于其他用途。

我的输出如下，这就是我想要的。但是时不时地，它会在显示此内容后崩溃:

   'Well!' thought Alice to herself, 'after such a fall as this, I shall think n
othing of tumbling down stairs!'

longest word in string is 8 letters long.
<<'Well!'>>
<<thought>>
<<Alice>>
<<to>>
<<herself,>>
<<'after>>
<<such>>
<<a>>
<<fall>>
<<as>>
<<this,>>
<<I>>
<<shall>>
<<think>>
<<nothing>>
<<of>>
<<tumbling>>
<<down>>
<<stairs!'>>
Process returned 0 (0x0)   execution time : 0.062 s
Press any key to continue.

Answer 1

while(!isspace(str[i]))如果字符串不以空格结尾，则永远不会终止。

段错误可能取决于在字符串末尾后空白在垃圾中出现之前需要多长时间。

相反，你可以做 while( i < wordscout ) .注意 l是多余的，你可以并且应该使用 wordscout - i .