C ++文件i / o错误？ [英] C++ file i/o error?

问题描述

为什么所有内容都被读为0？

Why is everything being read as 0?

    int width = 5;
    int height = 5;
    int someTile = 1;
    char buff[128];


    ifstream file("test.txt", ios::in|ios::binary);

    if(file.is_open())
    {
        cout << "open";
    }

    file.read(buff, sizeof(int));
    width = atoi(buff);

    file.read(buff, sizeof(int));
    height = atoi(buff);

    for (int x = 0; x < width; x++) {
        for (int y = 0; y < height; y++) {
            file.read(buff, sizeof(int));
            someTile = atoi(buff);
            cout << someTile;
        }
    }

我的文件格式代码是C＃，写得像这样：

My file format code is in C# and written like this:

FileStream stream = new FileStream("test.txt", FileMode.Create);
            BinaryWriter writer = new BinaryWriter(stream);
            // write a line of text to the file

            writer.Write(15);
            writer.Write(5);

            for (int i = 0; i < 15; i++)
            {
                for (int j = 0; j < 5; j++)
                {
                    writer.Write(1);
                }
            }

            // close the stream
            writer.Close();

推荐答案

在不知道test.txt的内容的情况下，很难确切地说，但看起来你反复在字符缓冲区/字符串中读取4个字节（大多数平台上的int的大小），然后尝试将其转换为数字。除非您的文件完全由四个以空字符结尾的字节块构成，否则我不希望这样做。

Without knowing the contents of test.txt it's difficult to say exactly, but it looks like you're repeatedly reading 4 bytes (size of an int on most platforms) into a character buffer / string, and then trying to turn that into a number. Unless your file is constructed entirely of four byte blocks that are null-terminated, I wouldn't expect this to work.

更新：好的，看看你的文件格式你你不是在写字符串，而是在写一些内容。因此，我希望您能够直接读取您的号码，而无需 atoi 。

Update: Ok, looking at your file format you're not writing strings, you're writing ints. Therefore I'd expect you to be able to read your numbers straight back in, with no need for atoi.

例如：

int value;
file.read((char*)&value, sizeof(int));

value 现在应包含来自文件。要转换整个示例，您需要查找以下内容：

value should now contain the number from the file. To convert your whole example you're looking for something like this:

int width = 5;
int height = 5;
int someTile = 1;

ifstream file("test.txt", ios::in|ios::binary);

if(file.is_open())
{
    cout << "open";

    file.read(reinterpret_cast<char*>(&width), sizeof(int));
    file.read(reinterpret_cast<char*>(&height), sizeof(int));

    for (int x = 0; x < width; x++) {
        for (int y = 0; y < height; y++) {
            file.read(reinterpret_cast<char*>(&someTime), sizeof(int));
            cout << someTile;
        }
    }
}

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