c - 在 C 中用 fread 和 fwrite 提问

Question

以下是我的代码，用于将一些硬编码的 int 值 (1,2,3,4,5) 写入文件，关闭该文件，以读取模式打开同一文件并读取写入的元素。从输出中可以看出，fwrite 正确发生，但 fread 读取不正确。

#include<stdio.h>
int main()
{

    FILE *fptr;
    FILE *optr;
    const char *filepath = "E:\\testinput.txt";

              int buf[5]={1,2,3,4,5};
    int obuf[5];
         int value;
    int *ptr = &value;

     int num_bytes_read;

    int no_of_iterations;


    int i;

    int ret;//return value for fwrite

    int count = 0;

    no_of_iterations = 5;

    //open the file

    fptr = fopen(filepath, "wb");
    if(fptr == NULL){
       printf("error in opening input file");
    }

    /*optr = fopen(outFilepath, "wb");
    if(optr == NULL){
           printf("error in opening output file");
    }*/



    printf("int %d ", sizeof(int));

    for(i=0;i<5;i++){
        printf("writing %d",buf[i]);
    ret = fwrite(buf,sizeof(int),1,fptr);
     if(ret != 1)
     {
         printf("error in fwrite:%d\n", ret);
     }
    }
    //written to input file
    fclose(fptr);
    fptr = fopen(filepath, "rb");
            if(fptr == NULL){
               printf("error in opening input file");
            }

    for(i=0;i<5;i++){

            //reading from input file
           num_bytes_read = fread(ptr,sizeof(int),1,fptr);
           if(num_bytes_read == 1){


           obuf[i] = *ptr;//storing into buf what is read from file
           printf("read successful: %d\n", obuf[i]);
           count++;
           }
           else{
               count = 99;
            break;
           }


         printf("\ncount%d", count);

  }


  fclose(fptr);

  return 0;


}

写入的输入文件，如果手动打开(在任何文本编辑器中)看到 5 个非字母数字字符(重复相同的符号)这是 Eclipse 中的输出

int 4 writing 1writing 2writing 3writing 4writing 5read successful: 1

count1read successful: 1

count2read successful: 1

count3read successful: 1

count4read successful: 1

count5

Answer 1

问题出在这一行:

ret = fwrite(buf,sizeof(int),1,fptr);

对 fwrite 的所有 5 次调用都具有相同的缓冲区地址，因此每次写入数组的第一个元素时都是 1。

由于要将所有数组元素一一写入，将buf+i作为起始地址传递给fwrite:

ret = fwrite(buf+i,sizeof(int),1,fptr);

现在fwrite得到的缓冲区起始地址就是数组中第i个元素的地址。