Question

将数据库中的值放入数组并将值发送到函数本身的addReader之后，这些值将成功存储，但是当返回main时，输入的值将消失。

给出以下代码：使用realloc

创建动态数组

reader* readerBuilder(reader *rdr, int *readNum){       //building all the readers
    FILE *read;
    int i=1;
    char *str;
    read = fopen("Readers.txt","r");
    checkFile(read);
    str = readFromFile(read);
    while(str != NULL)
    {
        rdr[i-1] = *cutToRdr(str);
        str = readFromFile(read);
        if(str != NULL){
            i++;
            rdr = (reader*)realloc(rdr,sizeof(reader)*i);
            checkreader(rdr);
        }
    }
    fclose(read);
    *readNum = i;
    return rdr;
}

给定调用函数：

reader* addReader(reader *rdr, int *readNum){       //adding a reader from the user
    char string[1000];
    rdr = (reader*)realloc(rdr,sizeof(reader)*(*readNum+1));// build new struct array ( bigger), with the old values
    checkreader(rdr);// check if can get memory
    printf("please enter the I.D. of the student you want to add:\n");
    scanf("%s",string);// get from operant
    rdr[*readNum].id=cutToStr(string);// put id in struct
    printf("please add the reader's first name:\n");
    scanf("%s",string);// get from operant
    rdr[*readNum].first_name=cutToStr(string);// put first name in struct
    printf("please add the reader's last name:\n");
    scanf("%s",string);// get from operant
    rdr[*readNum].last_name=cutToStr(string);// put last name in struct
    printf("please add the reader's address:\n");
    scanf("%s",string);// get from operant
    rdr[*readNum].address=cutToStr(string);// put adress in struct
    printf("please add the reader's phone:\n");
    scanf("%s",string);// get from operant
    rdr[*readNum].phone=cutToStr(string);// put phone in struct
    rdr[*readNum].numToTake = 5;// change value of numbers to tke to 5
    *readNum = *readNum + 1;// rise the number of the readers
    return rdr;// return the new structs array
}

鉴于在main中调用函数：

rdr=addReader(rdr,readNum);

读者结构的定义：

typedef struct reader{
    int numToTake;
    char *first_name, *last_name, *address, *phone, *id;
}reader;

我做错了什么？的问候，大卫

EDIT！

仍然无效。新版代码：

void addReader(reader **rdr, int *readNum){     //adding a reader from the user
    char string[1000];
    rdr = (reader**)realloc(rdr,sizeof(reader*)*(*readNum+1));// build new struct array ( bigger), with the old values
    checkreader(*rdr);// check if can get memory
    printf("please enter the I.D. of the student you want to add:\n");
    scanf("%s",string);// get from operant
    rdr[*readNum]->id=cutToStr(string);// put id in struct
    printf("please add the reader's first name:\n");
    scanf("%s",string);// get from operant
    rdr[*readNum]->first_name=cutToStr(string);// put first name in struct
    printf("please add the reader's last name:\n");
    scanf("%s",string);// get from operant
    rdr[*readNum]->last_name=cutToStr(string);// put last name in struct
    printf("please add the reader's address:\n");
    scanf("%s",string);// get from operant
    rdr[*readNum]->address=cutToStr(string);// put adress in struct
    printf("please add the reader's phone:\n");
    scanf("%s",string);// get from operant
    rdr[*readNum]->phone=cutToStr(string);// put phone in struct
    rdr[*readNum]->numToTake = 5;// change value of numbers to tke to 5
    *readNum = *readNum + 1;// rise the number of the readers
    //return rdr;// return the new structs array

}

主要的新呼叫：

addReader(&rdr,readNum);

Answer 1

你应该通过**rdr：

reader* addReader(reader **rdr, int *readNum)
                         ^^

此外，这会在您realloc时添加新的间接级别。

使用代码，您现在可以在指针的副本上realloc而不是实际的指针。

退出函数后，使用realloc不会在数组中存储值

1 个答案: