C++ IO二进制文件流：未指定输出时的默认值

发布于 2024-11-14 05:31:24 字数 675 浏览 4 评论 0原文

我的问题是关于二进制文件 I/O。假设运行以下代码：

#include <iostream>
#inclide <fstream>

int main(){
    fstream out;
    out.open("binfile.bin",ios::binary|ios::out);
    if(!out.good()){
        cout<<"ain't good"<<endl;
        return EXIT_FAILURE;
    }
    out.seekp(3);
    out<<char(74);
    out.seekp(7);
    out<<char(73);
    out.close();
}

binfile.bin 包含 00 00 00 4A 00 00 00 49，正如预期的那样。如果我不指定输出内容，我可以以某种方式更改放入文件中的默认值吗？我想将 00 替换为 30 之类的内容，以便 binfile.bin 包含 30 30 30 4A 30 30 30 49，是这样吗可行吗？当然，我可以在末尾循环遍历文件，并将所有 00 替换为 30，但我想避免这种情况。

原文

My question is about binary file I/O. Suppose the following code is run:

#include <iostream>
#inclide <fstream>

int main(){
    fstream out;
    out.open("binfile.bin",ios::binary|ios::out);
    if(!out.good()){
        cout<<"ain't good"<<endl;
        return EXIT_FAILURE;
    }
    out.seekp(3);
    out<<char(74);
    out.seekp(7);
    out<<char(73);
    out.close();
}

binfile.bin contains 00 00 00 4A 00 00 00 49, as expected. Can I somehow change that default value that is placed into the file if I don't specify what to output? I would like to replace 00 with something like 30, so that binfile.bin would contain 30 30 30 4A 30 30 30 49, is that doable? Of course I can loop through the file at the end and replace all 00s with 30s, but I'd like to avoid that.

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流年已逝 2024-11-21 05:31:24

您可以为 seekp 编写一个包装器并使用它。伪代码：

my_seekp(fstream& f, int pos)
{
    seek to end
    endpos = position at end
    if (pos > endpos)
    {
        int n = endpos - pos;
        for (int i = 0; i < n; ++i)
            f.put(char(30));
    }
    else
        seek to pos
}

You could write a wrapper for seekp and use that. Pseudocode:

my_seekp(fstream& f, int pos)
{
    seek to end
    endpos = position at end
    if (pos > endpos)
    {
        int n = endpos - pos;
        for (int i = 0; i < n; ++i)
            f.put(char(30));
    }
    else
        seek to pos
}

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