如何从 C++ 文件中读取小端整数？
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How to read little endian integers from file in C++?
提问by user1713700
Say I have a binary file; it contains positive binary numbers, but written in little endianas 32-bit integers
假设我有一个二进制文件；它包含正二进制数，但以小端字节序写成 32 位整数
How do I read this file? I have this right now.
我如何阅读这个文件？我现在有这个。
int main() {
FILE * fp;
char buffer[4];
int num = 0;
fp=fopen("file.txt","rb");
while ( fread(&buffer, 1, 4,fp) != 0) {
// I think buffer should be 32 bit integer I read,
// how can I let num equal to 32 bit little endian integer?
}
// Say I just want to get the sum of all these binary little endian integers,
// is there an another way to make read and get sum faster since it's all
// binary, shouldnt it be faster if i just add in binary? not sure..
return 0;
}
回答by Vaughn Cato
This is one way to do it that works on either big-endian or little-endian architectures:
这是一种适用于大端或小端架构的方法：
int main() {
unsigned char bytes[4];
int sum = 0;
FILE *fp=fopen("file.txt","rb");
while ( fread(bytes, 4, 1,fp) != 0) {
sum += bytes[0] | (bytes[1]<<8) | (bytes[2]<<16) | (bytes[3]<<24);
}
return 0;
}
回答by Kylo
回答by Reunanen
From CodeGuru:
来自CodeGuru：
inline void endian_swap(unsigned int& x)
{
x = (x>>24) |
((x<<8) & 0x00FF0000) |
((x>>8) & 0x0000FF00) |
(x<<24);
}
So, you can read directly to unsigned intand then just call this.
所以，你可以直接读取unsigned int，然后调用它。
while ( fread(&num, 1, 4,fp) != 0) {
endian_swap(num);
// conversion done; then use num
}
