c - 写入和读取二进制文件时出现问题

Question

我正在尝试创建一个合成数据集(值介于 0-1 之间)并将它们保存在二进制文件中。以下是我的代码:

int n = 4000, dim = 4,i,j;
FILE *fp=fopen("dataset.data", "w+");
double *data = (double *) calloc(n * dim, sizeof(double));
double *data_to_read = (double *) calloc(n * dim, sizeof(double));

// Generate dataset
srand(1);
for (i = 0; i < (n * dim); ++i) {
    data[i] = (float) rand() / (float) RAND_MAX;
}

// Writing to binary file
if (fp) fwrite(data, 1, (n*dim) * sizeof(double), fp);
else { printf("Something went wrong while writing to File !!  \n"); }

// To make sure data have been written, read and print out the file. 
fp = fopen("Home/dataset.data", "rb");
fread(data_to_read, 1, (n*dim) * sizeof(double), fp);
fclose(fp);

for (i = 0; i < n; ++i) {
    printf("[%d] ", i);
    for (j = 0; j < dim; ++j) {
        printf("%f, ", data_to_read[i * dim + j]);
    }
    printf("\n");
}

但是，我在打印结束时得到了很多零，这让我觉得有些地方不对劲。像这样:

[3962] 0.519062, 0.877532, 0.686047, 0.396526, 
[3963] 0.419497, 0.494090, 0.163209, 0.061352, 
[3964] 0.144232, 0.113827, 0.082452, 0.777153, 
[3965] 0.609784, 0.647998, 0.902744, 0.414265, 
[3966] 0.543551, 0.462175, 0.775620, 0.842364, 
[3967] 0.607382, 0.274029, 0.599672, 0.682604, 
[3968] 0.000000, 0.000000, 0.000000, 0.000000, 
[3969] 0.000000, 0.000000, 0.000000, 0.000000, 
[3970] 0.000000, 0.000000, 0.000000, 0.000000, 
[3971] 0.000000, 0.000000, 0.000000, 0.000000, 
[3972] 0.000000, 0.000000, 0.000000, 0.000000, 
[3973] 0.000000, 0.000000, 0.000000, 0.000000, 
[3974] 0.000000, 0.000000, 0.000000, 0.000000, 
[3975] 0.000000, 0.000000, 0.000000, 0.000000, 
[3976] 0.000000, 0.000000, 0.000000, 0.000000, 
[3977] 0.000000, 0.000000, 0.000000, 0.000000, 
[3978] 0.000000, 0.000000, 0.000000, 0.000000, 
[3979] 0.000000, 0.000000, 0.000000, 0.000000, 
[3980] 0.000000, 0.000000, 0.000000, 0.000000, 
[3981] 0.000000, 0.000000, 0.000000, 0.000000, 
[3982] 0.000000, 0.000000, 0.000000, 0.000000, 
[3983] 0.000000, 0.000000, 0.000000, 0.000000, 
[3984] 0.000000, 0.000000, 0.000000, 0.000000, 
[3985] 0.000000, 0.000000, 0.000000, 0.000000, 
[3986] 0.000000, 0.000000, 0.000000, 0.000000, 
[3987] 0.000000, 0.000000, 0.000000, 0.000000, 
[3988] 0.000000, 0.000000, 0.000000, 0.000000, 
[3989] 0.000000, 0.000000, 0.000000, 0.000000, 
[3990] 0.000000, 0.000000, 0.000000, 0.000000, 
[3991] 0.000000, 0.000000, 0.000000, 0.000000, 
[3992] 0.000000, 0.000000, 0.000000, 0.000000, 
[3993] 0.000000, 0.000000, 0.000000, 0.000000, 
[3994] 0.000000, 0.000000, 0.000000, 0.000000, 
[3995] 0.000000, 0.000000, 0.000000, 0.000000, 
[3996] 0.000000, 0.000000, 0.000000, 0.000000, 
[3997] 0.000000, 0.000000, 0.000000, 0.000000, 
[3998] 0.000000, 0.000000, 0.000000, 0.000000, 
[3999] 0.000000, 0.000000, 0.000000, 0.000000,

不知道我的写法对不对。任何帮助都是适用的。

Answer 1

你的代码有几个问题:

• 你不是fclose写入文件后立即访问该文件。
• 您没有检查所有 fopen如果他们成功了。
• 您需要使用“wb”而不是“w+”打开文件。
• 你读的文件和你写的不是同一个文件。
• 如果无法打开文件进行写入，则会显示错误消息，但您仍会继续尝试从无法打开的文件中读取

更正程序(包括更正无意义的注释和可疑的错误消息)，注释为<<是我的:

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

int main()
{
  int n = 4000, dim = 4, i, j;
  FILE *fp = fopen("dataset.data", "wb");                   // <<  wee need "wb" here
  double *data = calloc(n * dim, sizeof(double));          // << no casts in C
  double *data_to_read = calloc(n * dim, sizeof(double));

  // Generate dataset
  srand(1);
  for (i = 0; i < (n * dim); ++i) {
    data[i] = (float)rand() / (float)RAND_MAX;
  }

  // Writing to binary file
  if (fp)
    fwrite(data, 1, (n*dim) * sizeof(double), fp);
  else 
  {
    printf("Something went wrong while opening the file to write !!  \n"); 
    return 1;                     // << abort of file could not be opened
  }

  fclose(fp);                     // << closing file

  // Read and print out the file. 
  fp = fopen("dataset.data", "rb");  // << opening the same file than the one we wrote to

  if (fp)                          // << checking if file could be opened
  {
    fread(data_to_read, 1, (n*dim) * sizeof(double), fp);
    fclose(fp);

    for (i = 0; i < n; ++i) {
      printf("[%d] ", i);
      for (j = 0; j < dim; ++j) {
        printf("%f, ", data_to_read[i * dim + j]);
      }
      printf("\n");
    }
  }
  else
  {
    printf("Something went wrong while opening the file to read!!  \n");
    return 1;
  }

  // << check if read data is equal to written data

  if (memcmp(data_to_read, data, n*dim) == 0)
  {
    printf("\nRead data is equal to written data\n");
  }

  return 0;
}

免责声明:可能还有其他我没有注意到的错误。