如何在C中使用两个32位整数作为64位？

Question

我正在使用一个库,该库返回一个带有时间戳的结构,该时间戳由两个(TimestampHi,TimestampLo)unsigned longs表示.我几乎只需要打印出%lluprintf中的时间戳.

从这两个整数中获取数据并将其正确用作uint64_t的最简单方法是什么？

Answer 1

假设unsigned long long您的平台上是64位类型

assert(sizeof(unsigned long) * CHAR_BIT == 32);
assert(sizeof(unsigned long long) * CHAR_BIT == 64);
// Static asserts are more appropriate in cases like this

unsigned long long Timestamp = TimestampHi;
Timestamp <<= 32; Timestamp += TimestampLo; 

然后打印该Timestamp值.

与单线相同的东西

unsigned long long Timestamp = ((unsigned long long) TimestampHi << 32) + TimestampLo; 

或者干脆

printf("%llu\n", ((unsigned long long) TimestampHi << 32) + TimestampLo);

如果您希望从基于位的操作中抽象代码,则可以将表达式重写为

TimestampHi * ((unsigned long long) ULONG_MAX + 1) + TimestampLo