C++ 使用 write() 将无符号字符写入二进制文件
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Writing unsigned chars to a binary file using write()
提问by c0da
I was making a program that read binary files. So, I read the individual bytes into unsigned chars (actually reading the data as chars and casting them to unsigned chars for each character). Now I have to write back the unsigned chars to the binary file.
我正在制作一个读取二进制文件的程序。因此，我将单个字节读入无符号字符（实际上将数据作为字符读取并将它们转换为每个字符的无符号字符）。现在我必须将无符号字符写回二进制文件。
The problem is that now I am forced to write individual bytes after casting them to chars (because write() for binary files expects char* buffer). So, now i have to do the following:
问题是现在我被迫在将它们转换为字符后写入单个字节（因为二进制文件的 write() 需要 char* 缓冲区）。所以，现在我必须执行以下操作：
for(int x=0; x<data_size; x++)
{
ch=(char)data[x];
outfile.write(&ch,1);
}
Is there any way to get around this thing so that the amount of I/O operations are reduced in case of reading and writing?
有什么办法可以解决这个问题，以便在读写的情况下减少 I/O 操作的数量？
回答by 6502
You can do the casting on a pointer...
您可以在指针上进行转换...
outfile.write((char *)&data[0], data_size);
the same can be done for reading (i.e. just pass a pointer to the first element of an array of unsigned char casting it to a pointer to char).
读取也可以这样做（即，只需传递一个指向 unsigned char 数组的第一个元素的指针，将其转换为指向 char 的指针）。
回答by Armen Tsirunyan
The type of outfileis ofstream, right? ofstreamis a typedeffor,
的类型outfile是ofstream，对吧？ofstream是typedef为了，
typedef std::basic_ofstream<char, std::char_traits<char> > ofstream;
You need your own typedef,
你需要自己的typedef，
typedef std::basic_ofstream<unsigned char, std::char_traits<unsigned char> > uofstream;
And then,
进而，
uofstream outfile(...);
outfile.write(data, data_size); //no need to cast
回答by Nobody
When datais of type unsigned char*or unsigned char[]and you just want to write the bits into the file do a pointer cast:
当data属于unsigned char*or类型unsigned char[]并且您只想将位写入文件时进行指针转换：
for(int x=0; x<data_size; x++)
{
outfile.write((char*)data + x, 1);
}
As casting removes the issue of one at a time writing:
由于铸造消除了一次写作的问题：
outfile.write((char*)data, data_size);
And you do it all at once. Note that this outdoes the type checking and therefore is not the best solution.
而且您可以一次性完成所有操作。请注意，这超出了类型检查，因此不是最佳解决方案。
