如何读取二进制文件并将其保存在管道中

发布于 2024-10-11 02:48:34 字数 468 浏览 2 评论 0原文

我使用下面的代码打开一个二进制文件 fp （该文件包含保存的二维数组）并将其放入管道中：

if ((fp=fopen("file", "rb"))==NULL) {
    printf("Cannot open file.\n");
}
if (fread(array, sizeof(int), 5*5, fp) != 5*5) {
    if (feof(fp))
        printf("Premature end of file.");
} else {
    printf("File read error fread.");
}

这是将其放入管道中的代码吗？

close(fd[0]);
if ((ch=fgetc(fp))==EOF)
    write(fd[1], &ch, 1 );

如果我想对数组求和，我该怎么做呢？

原文

I used the code below to open a binary file fp (the file contain a saved 2D array) and put it inside a pipe:

if ((fp=fopen("file", "rb"))==NULL) {
    printf("Cannot open file.\n");
}
if (fread(array, sizeof(int), 5*5, fp) != 5*5) {
    if (feof(fp))
        printf("Premature end of file.");
} else {
    printf("File read error fread.");
}

Is this the code to put it inside the pipe?

close(fd[0]);
if ((ch=fgetc(fp))==EOF)
    write(fd[1], &ch, 1 );

If I want to make a sum of the array, how could I make it?

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迷荒 2024-10-18 02:48:34

只要大小保持较小，将数组写入管道的最明智的方法是：（

int nw = 5 * 5 * sizeof(int);
if (write(fd[1], array, nw) != nw)
    err_exit("Failed to write to pipe");

其中 err_exit() 是一个将消息写入标准错误并退出的函数（或不返回。）

这假设你的数组是一个 5x5 数组（你的注释暗示它是 10x2，在这种情况下你的读取代码有重大问题）它假设管道中缓冲区的大小足够大。保存数据；如果不是，您的写入调用可能会阻塞。 SIGPIPE 信号，由于 close(fd[0]); 的缘故，

可以一次写入一个字节 -

从 < 中一次读取一个字节的性能并不理想。在将数据读入 array 后，执行 code>fp 并不完全明智 - 您最多只是读取不同的数据以写入管道，

这是对 2D 数组求和的正常方法。 is (C99)：

enum { DIM_1 = 5, DIM_2 = 5 };
int array[DIM_1][DIM_2];

...data to load array...

int sum = 0;
for (int i = 0; i < DIM_1; i++)
{
    for (int j = 0; j < DIM_2; j++)
         sum += array[i][j];
}

数据来自哪里并不重要，只要你实际初始化它即可。

The most sensible way to write the array to the pipe, as long as the size remains small, is to do:

int nw = 5 * 5 * sizeof(int);
if (write(fd[1], array, nw) != nw)
    err_exit("Failed to write to pipe");

(Where err_exit() is a function that writes a message to standard error and exits (or does not return.)

This assumes that your array is a 5x5 array (a comment from you implies it is 10x2, in which case your reading code has major problems). It assumes that the size of the buffer in a pipe is big enough to hold the data; if it is not, your write call may block. It assumes that there is somewhere a process to read from the pipe; if this is the only process, the write() will trigger a SIGPIPE signal, killing your process, because of the close(fd[0]);.

Writing one byte at a time is possible - it is not stellar for performance.

Reading one byte at a time from fp after you've already read the data into array is not entirely sensible - you are at best reading different data for writing to the pipe.

The normal way of summing a 2D array is (C99):

enum { DIM_1 = 5, DIM_2 = 5 };
int array[DIM_1][DIM_2];

...data to load array...

int sum = 0;
for (int i = 0; i < DIM_1; i++)
{
    for (int j = 0; j < DIM_2; j++)
         sum += array[i][j];
}

It doesn't matter where the data came from, just so long as you actually initialized it.

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