c++ - gmtime 同时改变两个指针

Question

我有这个代码:

time_t tt = time(NULL);
tm* currentTime = gmtime(&tt);
tm* storedTime = gmtime(&m_time);

其中m_time是构造时的一个time_t成员数据集。当我用这个数据成员设置 storedTime 时，当前时间获得相同的值，就好像两个 tm 指针指向同一个变量一样。这是预期的行为吗？我怎么能分开 tm 结构来比较时间？

谢谢

Answer 1

来自关于 gmtime 的文档:

This structure is statically allocated and shared by the functions gmtime and localtime. Each time either one of these functions is called the contents of this structure is overwritten.

使用此代码创建拷贝:

time_t tt = time(NULL);

tm currentTime = *gmtime(&tt);
tm storedTime = *gmtime(&m_time);

(此处的指针引用等同于 memcpy(&currentTime, gmtime(&tt), sizeof(tm)))