std::string::reserve() - 未名空间MITBBS历史存档

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std::string::reserve()

std::string::reserve()# Programming - 葵花宝典

t*d2007-10-20 07:10

1 楼

看到网上一个解释：
void reserve(uint res_arg = 0)
change the capacity of a String to the maximum of res_arg and size(). This
may be an increase or a decrease in the capacity.
这个对吗？我做了个简单的测试，跟踪 i 的值，但是在reserve前后没有变化，哪位
指点一下，谢谢了。
std::string str1("abcdefgh");
int i=str1.size(); // 结果是8
i=str1.capacity(); // 结果是15
str1.reserve(4);
i=str1.capacity(); // 结果是15
i=str1.size(); // 结果是8

t*t2007-10-20 07:10

2 楼

official document is as follows:
void reserve(size_type res_arg=0);
1 The member function reserve() is a directive that informs a
basic_string object of a planned change in size, so that it can manage
the storage allocation accordingly.
Effects:
After reserve(), capacity() is greater or equal to the argument of
reserve. [Note: Calling reserve() with a res_arg argument less than
capacity() is in effect a non-binding shrink request. A call with
res_arg <=

【在 t****d 的大作中提到】

: 看到网上一个解释：
: void reserve(uint res_arg = 0)
: change the capacity of a String to the maximum of res_arg and size(). This
: may be an increase or a decrease in the capacity.
: 这个对吗？我做了个简单的测试，跟踪 i 的值，但是在reserve前后没有变化，哪位
: 指点一下，谢谢了。
: std::string str1("abcdefgh");
: int i=str1.size(); // 结果是8
: i=str1.capacity(); // 结果是15
: str1.reserve(4);