我想用开辟堆空间实现拷贝操作，但程序不知道错在哪

我想用开辟堆空间实现拷贝操作，但程序不知道错在哪

#define _CRT_SECURE_NO_WARNINGS
#include
#include

int Cfile(char* p, char* filename)
{
    FILE* pf = fopen(filename, "r");
    if (pf == NULL)
    {
        perror("fopen");
        return -1;
    }
    //使用文件
    int temp = 1024;
    int i = 0;
    while (fread(p + i, sizeof(char), 1, pf))
    {
        if (i == temp-1)
        {
            char* p1 = (char*)realloc(p, sizeof(char) * (temp + 1024));
            if (p1 != NULL)
            {
                p = p1;
                p1 = NULL;
                temp += 1024;
                printf("增容成功\n");
            }
            else
            {
                printf("增容失败\n");
                perror("realloc");
                return -1;
            }
        }

        i++;
    }
    //关闭文件
    fclose(pf);
    pf = NULL;
    return i;

}

void Vfile(char* p, char* filename,int n)
{
    FILE* pf = fopen(filename, "w");
    if (pf == NULL)
    {
        perror("fopen");
        return -1;
    }
    //使用文件
    for (int i = 0;i < n;i++)
    {
        fwrite(p+i, sizeof(char), 1, pf);
    }
    //关闭文件
    fclose(pf);
    pf = NULL;

}

int main()
{
    char cfilename[] = "C:\\Users\\zhizhu\\Desktop\\hello\\文件拷贝.txt";
    char vfilename[] = "C:\\Users\\zhizhu\\Desktop\\hello\\文件拷贝2.txt";
    char* p = (char*)malloc(sizeof(char) * 1024);
    int n = Cfile(p, cfilename);
    Vfile(p, vfilename, n);
    free(p);
    p = NULL;
}

实现过程中传入的形参char* p读取到数据内容后并没能传递到实参上去，那么Vfile函数中参数为空，导致报错。
改为内部创建内存，传出数据外部使用和释放。

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<stdlib.h>
 
char* Cfile(int& n, char* filename)
{
    if (filename == NULL)
    {
        return NULL;
    }
    FILE* pf = fopen(filename, "r");
    if (pf == NULL)
    {
        perror("fopen");
        return NULL;
    }
    char* p = (char*)malloc(sizeof(char) * 1024);
    //使用文件
    int temp = 1024;
    int i = 0;
    while (fread(p + i, sizeof(char), 1, pf))
    {
        if (i == temp-1)
        {
            char* p1 = (char*)realloc(p, sizeof(char) * (temp + 1024));
            if (p1 != NULL)
            {
                p = p1;
                p1 = NULL;
                temp += 1024;
                printf("增容成功\n");
            }
            else
            {
                printf("增容失败\n");
                perror("realloc");
                return NULL;
            }
        }
 
        i++;
    }
    //关闭文件
    fclose(pf);
    pf = NULL;
    n = i;
    return p;
 
}
 
void Vfile(char* p, char* filename,int n)
{
    if (p == NULL)
    {
        return ;
    }
    FILE* pf = fopen(filename, "w");
    if (pf == NULL)
    {
        perror("fopen");
        return ;
    }
    //使用文件
    for (int i = 0;i < n;i++)
    {
        fwrite(p+i, sizeof(char), 1, pf);
    }
    //关闭文件
    fclose(pf);
    pf = NULL;
 
}
 
int main()
{
    char cfilename[] = "C:\\Users\\zhizhu\\Desktop\\hello\\文件拷贝.txt";
    char vfilename[] = "C:\\Users\\zhizhu\\Desktop\\hello\\文件拷贝2.txt";
    
    int n = 0;
    char* p = Cfile(n, cfilename);
    Vfile(p, vfilename, n);
    free(p);
    p = NULL;
    return 0;
}