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c - C 中的数组地址有问题？

问题描述

我创建了一个动态数组名称 listProduct，现在我想从文件中读取数据并插入到这个数组中。但是我在解析数组时遇到了一些麻烦，我知道我解析了错误的地址:(但我无法解决这个问题。有人可以帮助我（我花了 3 个小时，但没有用）。谢谢全部

在主（）

int main(int argc, char** argv) {

    struct Product* listProduct = (struct Product*) malloc(sizeof(struct Product) * 1); 
    printf("address of listProduct in main: %d \n", &listProduct);
    int length = 0;
    char fileName[] = "products.txt";
    length = readDataFromFile(&listProduct,length,fileName);    
    
    printf("address of listProduct in main after insert \n: %d \n", &listProduct);
    printf("length in main %d \n", length);
    printf("start for in main \n");
    int i;
    for(i =0; i < length; i++){
        printf("%s \n", listProduct[i].tenSanPham);
    }
        
    printf("end for in main \n");   
    return 0;
}

在 readFile 函数中

int readDataFromFile(struct Product* listProduct,int length, char fileName[]){
    printf("address of listProduct in readData: %d \n", (*listProduct));
    FILE *fp;
   char buff[1024];
    struct Product product;
   fp = fopen(fileName, "r");

   while(fgets(buff, 255, (FILE*)fp) != NULL){
        product = convertStringToProduct(buff);
        printf("IN readData: %s \n", product.tenSanPham);
        insertProduct(product, &(*listProduct), length);
        length++;
   }
    fclose(fp); 
   int i ;
   printf("\n\ncheck value in listProduct after insert\n");
   for(i = 0; i < length; i++){
    printf("IN FOREACH readData: %s \n", listProduct[i].tenSanPham);
   }  
    printf("read done \n");
    return length;
}

在插入函数中

void insertProduct(struct Product product, struct Product** listProduct, int length)
{
    printf("addres of listProduct in insert %d \n", (*listProduct));
    printf("Product In Insert: %s \n", product.tenSanPham);
  *listProduct = (struct Product*) realloc(listProduct, sizeof(struct Product) * (length+1));
  (*listProduct)[length] = product;
  printf("Get product inserted: %s length: %d \n", (*listProduct)[length].tenSanPham, length);
  printf("insert done!\n");
}

安慰：

address of listProduct in main: 6487568
address of listProduct in readData: 6486368
IN readData: FOOD 1
addres of listProduct in insert 1905632
Product In Insert: FOOD 1

--------------------------------
Process exited after 0.5239 seconds with return value 3221226356
Press any key to continue . . .

标签： cpointers

解决方案

你有很多错误。通过启用编译器警告可以找到其中的一些。编译时使用-Wall -Wextra -pedantic(gcc/clang) 或您的编译器的等效项。

首先，realloc(listProduct, ...)应该是realloc(*listProduct, ...)。

其次，realloc可以返回与提供的地址不同的地址。这就是为什么insertProduct需要一个struct Product**. 这允许它改变调用者的指针。readDataFromFile需要做同样的事情。参数必须是struct Product **. 地址改变的事实不是问题。

这将顺便修复您当前遇到的许多错误。例如，&(*listProduct)将变得正确。但是，最好写成listProduct.

进行上述修复后，listProduct[i].tenSanPham将需要更改为(*listProduct)[i].tenSanPham.

%p用于指针，而不是%d. 他们（奇怪地）需要被强制转换void*为 for %p。

你不检查是否realloc成功fopen。

固定的：

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

struct Product { ... };

typedef struct Product Product;  // So we don't have to use "struct Product" everywhere.

Product convertStringToProduct(const char *s) {
    ...
}

void insertProduct(Product **listProductPtr, size_t *lengthPtr, Product product) {
    printf("[insertProduct] Address of variable in caller: %p\n", (void*)listProductPtr);
    if (*lengthPtr)
        printf("[insertProduct] Address of first product: %p\n", (void*)*listProductPtr);  // Same: &((*listProduct)[0])

    Product *tmp = realloc(*listProductPtr, sizeof(Product) * (*lengthPtr + 1));
    if (!tmp) {
       // ...
    }

    *listProductPtr = tmp;
    (*listProductPtr)[(*lengthPtr)++] = product;

    printf("[insertProduct] Address of variable in caller: %p\n", (void*)listProductPtr);
    if (*lengthPtr)
        printf("[insertProduct] Address of first product: %p\n", (void*)*listProductPtr);  // Same: &((*listProduct)[0])
}

void readDataFromFile(Product **listProductPtr, size_t *lengthPtr, const char *fileName) {
    printf("[readDataFromFile] Address of variable in caller: %p\n", (void*)listProductPtr);
    if (*lengthPtr)
        printf("[readDataFromFile] Address of first product: %p\n", (void*)*listProductPtr);  // Same: &((*listProduct)[0])

    FILE *fp = fopen(fileName, "r");
    if (!fp) {
       // ...
    }

    char buff[1024];
    while (fgets(buff, sizeof(buff), fp)) {
        Product product = convertStringToProduct(buff);
        insertProduct(listProductPtr, lengthPtr, product);
    }

    fclose(fp); 

    printf("[readDataFromFile] Address of variable in caller: %p\n", (void*)listProductPtr);
    if (*lengthPtr)
        printf("[readDataFromFile] Address of first product: %p\n", (void*)*listProductPtr);  // Same: &((*listProduct)[0])
}

int main(void) {
    Product *listProduct = NULL;
    size_t length = 0;

    printf("[main] Address of listProduct variable: %p\n", (void*)&listProduct);
    if (length)
        printf("[main] Address of first product: %p\n", (void*)listProduct);  // Same: &(listProduct[0])

    readDataFromFile(&listProduct, &length, "products.txt");
    
    printf("[main] Address of listProduct variable: %p\n", (void*)&listProduct);
    if (length)
        printf("[main] Address of first product: %p\n", (void*)listProduct);

    for (size_t i=0; i<length; ++i) {
        printf("%s\n", listProduct[i].tenSanPham);
    }
        
    return 0;
}

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