Question

我有以下代码：

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
struct wordlist {
    char *value;
    struct wordlist *next;
};
int compare (struct wordlist *one , struct wordlist *two) {
    return strcmp(one->value, two->value);
}
void add(struct wordlist *pp, char *value) {
    struct wordlist *new;
    new = malloc(sizeof(*new));
    new->value = value;
    for ( ; pp != NULL; pp = pp->next) {
        if (compare(pp, new) > 0 ) {
            break;
        }
    }
    new->next = pp;
    pp = new;
}
void display(struct wordlist *ptr) {
    for (; ptr != NULL; ptr = ptr->next) {
        printf("%s\n", ptr->value);
    }
}

在中间打破它以便提交。遗憾

int main(void) {
    struct wordlist *root = NULL;
    add(root, "item1");
    add(root, "item2");
    add(root, "item4");
    add(root, "item3");
    display(root);
    return 0;
}

它应该打印出来

item1 item2 item3 item4

但它不打印任何东西，我不明白为什么。

Answer 1

是否需要将指针传递给指针？

void add(struct wordlist **pp, char *value) {
struct wordlist *new;
new = malloc(sizeof(*new));
new->value = value;
for ( ; (*pp) != NULL; (*pp) = (*pp)->next) {
    if (compare((*pp), new) > 0 ) {
        break;
    }
}
new->next = (*pp);
(*pp) = new;
}

Answer 2

此方法不会更改root并且也可以正常工作。

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
struct wordlist {
    char *value;
    struct wordlist *next;
};

int compare (struct wordlist *one , struct wordlist *two) {
    return strcmp(one->value, two->value);
}

void add(struct wordlist *pp, char *value) {
    struct wordlist *new;

    new = malloc(sizeof(*new));
    new->value = value;

    for ( ; pp->next != NULL; pp = pp->next) {
        if (compare(pp->next, new) > 0 ) {
            break;
        }
    }
    new->next = pp->next;
    pp->next = new;

}
void display(struct wordlist *ptr) {
    while ( ptr->next != NULL ) {
        ptr = ptr->next;
        printf("%s\n", ptr->value);
    }
}

int main(void) {
    struct wordlist root;

    root.next = NULL;
    add(&root, "item1");
    add(&root, "item2");
    add(&root, "item4");
    add(&root, "item3");
    display(&root);
    return 0;
}

C字符串和指针

2 个答案: