[英]Reading DWORD from binary file
Why these lines of code doesn't work when i try to read a DWORD num = 1880762702
using fread(&num, "file path", 1, FILE*);
当我尝试使用
fread(&num, "file path", 1, FILE*);
读取DWORD num = 1880762702
时,为什么这些代码行不起作用fread(&num, "file path", 1, FILE*);
I get the result = 10574
if I change the num to any other number say 2880762702
only then it works. 我得到
result = 10574
如果我将数字更改为任何其他数字说2880762702
然后它才有效。
To read a multibyte quantity such as a DWORD (which is Win32-speak for a 32-bit number) you need to be aware of endianness . 要读取多字节数量(如DWORD(对于32位数字为Win32),您需要了解字节顺序 。 It's best to read the number one byte at a time, and convert from the byte ordering used in the file.
最好一次读取一个字节,并从文件中使用的字节顺序转换。
FILE *in;
DWORD num = 0;
if((fin = fopen("filename.bin", "rb")) != NULL)
{
unsigned char b0, b1, b2, b3;
fread(&b3, sizeof b3, 1, in);
fread(&b2, sizeof b2, 1, in);
fread(&b1, sizeof b1, 1, in);
fread(&b0, sizeof b0, 1, in);
// Assuming file is big-endian.
// for little endian, swap the order to b0...b3
num = (((DWORD) b3) << 24) | (((DWORD) b2) << 16) | (((DWORD) b1) << 8) | b0;
fclose(in);
}
The second parameter to fread()
is the size of the data you want to read. fread()
的第二个参数是您要读取的数据的大小。 In your case, that's sizeof(DWORD)
. 在你的情况下,这是
sizeof(DWORD)
。
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