将read()读取的数据写入C中的int数组 [英] Writing data read with read () to int array in C

问题描述

我有一个文件，每行都有数字.我正在尝试使用 read() 函数将从文件中读取的数据写入 int 数组.我可以读取文件并将其打印到终端.如何获取读入 arr 数组的数字?

I have a file with numbers on each line. I am trying to write the data read from the file to the int array with the read () function. I can read the file and print it to the terminal. How can i get the numbers i read into arr array ?

这是我的代码

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

int main() {
    int len, fd,arr[10000],i=0;
    fd = open("1.txt", O_RDONLY);
    if (fd >= 0) {

        while(read(fd, &len, sizeof(int)) > 0){
            write(1, &len, sizeof(int));

        }
    }

    close(fd);

    return 0;
}

推荐答案

在大多数(所有?)实现中，整数将数字的二进制表示存储在该整数的位和字节中.另一方面，字符串和诸如文本文件之类的东西使用字节来存储数字、空格和换行符的 ASCII 值.

On most (all?) implementations, a integer stores the binary representation of a number in the bits and bytes of that integer. In the other hand, a string and something like your text file uses bytes to store the ASCII value of digits, spaces and line feeds.

int(假设 4 个字节，每个字节 8 位，大端)可以这样存储值 1234:

int (assuming 4 byte with 8 bit each, big endian) may store the value 1234 this way:

Address   0x42  0x43  0x44  0x45
Value     0x00  0x00  0x04  0xD2
Text       NUL   NUL   EOT    Ò

另一方面，字符串可以包含代表文本的每个字符的 ASCII 值.字符串1234"可以这样存储:

In the other hand, a string can contain the ASCII values of each character that represents a text. The String "1234" could be stored like this:

Address   0x82  0x83  0x84  0x85  0x86
Value     0x31  0x32  0x33  0x34  0x00
Text        1     2     3     4    NUL

读取时，您读取文本文件的字符.将它们读入 char 数组很容易，您不需要进行任何对话，只需在末尾添加 NUL 字节即可.当你想得到数字时，你必须将它们从字符串中转换.

When you do a read, you read the characters of the text file. Reading them into a char array is easy, you do not need to do any conversation, only add the NUL-Byte at the end. When you want to get the number, you have to convert them from a string.

这意味着您必须读取文件，如果需要，您可以使用 read() 执行此操作，并将内容存储在 char 数组中，添加一个 NUL-Byte 然后使用类似 strtol() 或 sscanf() 的函数转换结果字符串.

This means you have to read the file, you can do this with read() if you want, and store the content in a char array, add a NUL-Byte and then convert the resulting string with a function like strtol() or sscanf().

您所做的是将 ASCII 字符读入 int len.当您在 write() 调用之前使用调试器时，您可以检查 len 的值.就我而言，我将其用作输入文件:

What you do is reading the ASCII characters into the int len. When you use a debugger before the write() call, you can check the value of len. In my case i used this as an input file:

0
1
2
3
...

当我在 write() 之前停止调试器时，我看到 len 的值为 170986032 == 0xA310A30.我的系统是小端的，这意味着最低字节存储在最低地址(与我之前的示例不同).这意味着 0x30 首先出现，然后是 0x0a、0x31 和 0x0A.由此我们知道我们得到了如下len的内存布局.

When i stop my debugger before write(), i see that len has the value of 170986032 == 0xA310A30. My system is little endian, means the lowest byte is stored at the lowest address (unlike my previous example). Which means 0x30 comes first, then 0x0a, 0x31 and 0x0A. From this we know that we got the following memory layout of len.

Address Offset   0x00  0x01  0x02  0x03
Value            0x30  0x0A  0x31  0x0A
Text                0    LF     1    LF

如您所见，文本被解释为 int.

As you can see, the text is interpreted as a int.

您想将数据存储到 char 数组中.然后解析它.我使用一些伪代码来更好地解释它.这不是 C 代码.您应该学习编写自己的代码.这只是为了让您了解您必须做什么:

You want to store the data into a char array. And then parse it. I use some pseudo code to explain it better. This is not C-Code. You should learn to write your own code. This is just to get you an idea what you have to do:

char buffer[<buffersize>] //create a buffer array
r=read(buffer) //read the file into the buffer. You may need to repeat that multiple times to get everything
if r==error //check for errors
  <do some error handling here>
buffer[<one after the last read byte>]='\0' //add the NUL-Byte st the end, so that we have a string.
int values[<number of ints you want>]  //create an array to store the parsed values
for(<one loop for every int>) //make the loop for every int, to parse the int
  values[<index>]=strtol(buffer,&buffer,0) //parse the text to a int
  if error occured:
    <do some error handling here>

如何在 C 中实现它是您的任务.请记住缓冲区大小，以免以 UB 结尾.

How to implement this in C is your task. Keep buffer sizes in mind so you do not end with UB.

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