Question

[注意我正在使用C] 我有一个问题，当我连续两次调用printf时，我得到＆＃34;垃圾数据＆＃34;第二次。第一个printf将打印出来＃ra; rajan1＆＃34;正如所料，第二个printf将打印出随机符号。我不确定它是随机的还是地址。有谁知道为什么我会收到这些结果？这是我的代码中的一个片段，它突出了我的问题（不是连续的printf语句：

void main(void)
{
    struct listNode **pStart = (struct listNode**) malloc(sizeof(struct listNode**));
    load(pStart);
    printf(" %s\n",*(*pStart)->data->artist);
    printf(" %s\n",*(*pStart)->data->artist);
}

正如我所说，输出是我第一次预期的字符串（它打印＆＃34; rajan1＆＃34;）和第二次随机的东西（ussually symbols）。我已经在互联网上搜索了类似问题，但我还没能找到一个。我的搜索表明我可能需要＆＃34;免费＆＃34;某个变量，但我不知道我需要释放什么，或者可能它是我不确定的编译器版本所独有的（我使用的是默认的c编译器在visual studio 2012 ultimate v11.0.61219.00更新5）。我已经包含了所有其他代码，因为希望有人可以重现这一点。最重要的是我的问题是在什么情况下printf语句可以改变一个值？

的main.c

#include "Header.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void main(void)
{
    struct listNode **pStart = (struct listNode**) malloc(sizeof(struct listNode**));
    load(pStart);
    printf(" %s\n",*(*pStart)->data->artist);
    printf(" %s\n",*(*pStart)->data->artist);
}

header.c

#include "Header.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void load(struct listNode **temp)
{
    struct listNode **head = (struct listNode**) malloc(sizeof(struct listNode**));
    FILE *pF;
    char artist[100];
    char album[100];
    char song[100];
    char genre[100];
    int ntp = 0;
    int rating = 0;
    int minutes = 0;
    int seconds = 0;
    pF = fopen("Songs.DATA", "r");
    *temp = NULL;
    *head = (struct listNode*) malloc(sizeof(struct listNode*));
    while (fscanf(pF, "%100[^,],%100[^,],%100[^,],%100[^,],%2[^,],%2[^,],%5[^,],%2[^,]", &artist, &album, &song, &genre, &minutes, &seconds, &ntp, &rating) == 8)
    {
        *head = makeNode(makeRecord(artist, album, song, genre, makeSongLength(minutes, seconds), ntp, rating));
        insertNode1(temp,head);
        *temp=*head;
    }
    fclose(pF);
}

struct listNode * makeNode ( struct record * newData)
{
    struct listNode mem;
    struct listNode * pMem = &mem;
    pMem = (struct listNode *) malloc (sizeof (struct listNode*));
    pMem->data = (struct record *) malloc (sizeof (struct record*));
    pMem->data = newData;
    pMem->pNext = (struct listNode *) malloc (sizeof (struct listNode*));
    pMem->pNext = pMem;
    pMem->pLast = (struct listNode *) malloc (sizeof (struct listNode*));
    pMem->pLast = pMem;
    return pMem;
}

struct record * makeRecord(char*artist,char *album,char *song,char *genre,struct songLength *length, int ntp, int rating)
{
    struct record * pMem = NULL;

    pMem = (struct record *) malloc (sizeof (struct record));
    *pMem->artist = (char *) malloc ((sizeof (char) *100)+1);
    *pMem->artist = artist;
    *pMem->album = (char *) malloc ((sizeof (char) *100)+1);
    *pMem->album = album;
    *pMem->song = (char *) malloc ((sizeof (char) *100)+1);
    *pMem->song = song;
    *pMem->genre = (char *) malloc ((sizeof (char) *100)+1);
    *pMem->genre = genre;
    pMem->length = (struct songLength *) malloc (sizeof (struct songLength));
    pMem->length = length;
    pMem->ntp = (int) malloc (sizeof (int));
    pMem->ntp = ntp;
    pMem->rating = (int) malloc (sizeof (int));
    pMem->rating = rating;

    return pMem;
}

void insertNode1(struct listNode ** old, struct listNode ** fresh)
{
    if (*old == NULL)
        {
            (*fresh)->pLast=*fresh;
            (*fresh)->pNext=*fresh;
            return;
        }
    if ((*fresh)->data->artist <= (*old)->data->artist )
        {
            (*fresh)->pLast=(*old)->pLast;printf("1\n");
            (*fresh)->pNext=(*old);printf("2\n");
            if ((*fresh)->pLast==NULL)
            {
                (*fresh)->pLast==*old;
            }
            (*fresh)->pLast->pNext=*fresh;printf("3\n");
            (*fresh)->pNext->pLast=*fresh;printf("4\n");
        }
    else insertNode1(&(*old)->pNext,fresh);
    return;
}

struct songLength * makeSongLength(int minutes, int seconds)
{
    struct songLength * pMem = NULL;

    pMem = (struct songLength *) malloc (sizeof (struct songLength));

    pMem->minutes = minutes;
    pMem->seconds = seconds;

    return pMem;
}

header.h

#ifndef Header_h
#define Header_h


void sort();
void load(struct listNode **temp);
void display(struct listNode **head);
struct listNode * makeNode ( struct record * newData);
struct record * makeRecord(char*artist,char *album,char *song,char *genre,struct songLength *length, int ntp, int rating);
struct songLength * makeSongLength(int minutes, int seconds);
void insertNode1(struct listNode ** old, struct listNode ** fresh);

/*A record is a struct type which consists of the following attributes:
*      Artist – a string
*      Album title – a string
*      Song title – a string
*      Genre – a string
*      Song length – a struct type consisting of seconds and minutes, both integers
*      Number times played – an integer
*      Rating – an integer (1 – 5)*/
/*typedef struct record
{
    char *artist[100];
    char *album[100];
    char *song[100];
    char *genre[100];
    struct songLength *length;
    int ntp;
    int rating;
};

typedef struct songLength
{
    int minutes;
    int seconds;
};

typedef struct listNode
{
    struct record * data;
    struct listNode * pNext;
    struct listNode * pLast;
};

#endif

最后我用来测试它的文本文件（songs.DATA）：

rajan1,summer india1,sweet summer1,pop1,21,31,01,11,
rajan2,summer india2,sweet summer2,pop2,22,32,02,12,

edit1：在header.c底部包含缺少的makeSongLength（）

Answer 1

 while (fscanf(pF, "%100[^,],%100[^,],%100[^,],%100[^,],%2[^,],%2[^,],%5[^,],%2[^,]", &artist, &album, &song, &genre, &minutes, &seconds, &ntp, &rating) == 8)

此行会导致 UB ，就像在这些数组中一样，您没有为null character留出空间。另外，格式说明符int也是%d。改为这个 -

while (fscanf(pF, " %99[^,],%99[^,],%99[^,],%99[^,],%d,%d,%d,%d,",artist, album,song,genre,&minutes, &seconds, &ntp, &rating) == 8)

void main(void) - ＆gt; int main(void)或int main(int argc,char **argv)

不要将malloc的结果投射到几乎所有情况下。

C语言结构在printf（）调用后更改值

1 个答案: