C++ vector的访问(resize,pu_back与下标访问的区别)
2015-05-08 10:39
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在编写代码时发现vector的一个现象
(1)
std::vector<std::string> str_vector;
str_vector.resize(3);
str_vector.push_back("name_1");
str_vector.push_back("name_2");
然后进行访问逐一打印发现:
for (std::vector<std::string>::iterator iter = str_vector.begin(); iter != str_vector.end(); ++iter)
{
std::cout<<*iter<<", ";
}
其值为:"","","","name_1","name_2",
此时发现resize是开辟了三个string空间,而后push_back是接着前面开辟的空间而往里push.
(2)
std::vector<std::string> str_vector;
str_vector.push_back("name_1");
str_vector.push_back("name_2");
其值为:"name_1","name_2",
(3)
std::vector<std::string> str_vector;
str_vector[0] = "name_1"; //wrong,错误,vector大小未知,且没有元素.
// 下标只能用于获取已存在的元素
总结:
(1) 若想对vector进行下面访问,则必须空间已开辟,可以用:
std::vector<std::string> str_vector;
str_vector.resize(3);
str_vector[0] = "name_1";
str_vector[1] = "name_2";
str_vector[2] = "name_3";
也可用:
std::vector<std::string> str_vector;
str_vector.push_back("name_1");
str_vector.push_back("name_2");
for(int i=0; i< str_vector.size(); i++)
{
std::cout<<str_vector[i]<<std::endl;
}
(2) 请注意resize()与push_back的同时使用,其空间是resize的空间+push_back的空间,否则达不到预设目标.
![](http://img.blog.csdn.net/20150528112002132?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvdzM4MzExNzYxMw==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center)
欢迎大家批评,指正,交流!
联系方式:
emai: tongzhuodenilove@163.com
(1)
std::vector<std::string> str_vector;
str_vector.resize(3);
str_vector.push_back("name_1");
str_vector.push_back("name_2");
然后进行访问逐一打印发现:
for (std::vector<std::string>::iterator iter = str_vector.begin(); iter != str_vector.end(); ++iter)
{
std::cout<<*iter<<", ";
}
其值为:"","","","name_1","name_2",
此时发现resize是开辟了三个string空间,而后push_back是接着前面开辟的空间而往里push.
(2)
std::vector<std::string> str_vector;
str_vector.push_back("name_1");
str_vector.push_back("name_2");
其值为:"name_1","name_2",
(3)
std::vector<std::string> str_vector;
str_vector[0] = "name_1"; //wrong,错误,vector大小未知,且没有元素.
// 下标只能用于获取已存在的元素
总结:
(1) 若想对vector进行下面访问,则必须空间已开辟,可以用:
std::vector<std::string> str_vector;
str_vector.resize(3);
str_vector[0] = "name_1";
str_vector[1] = "name_2";
str_vector[2] = "name_3";
也可用:
std::vector<std::string> str_vector;
str_vector.push_back("name_1");
str_vector.push_back("name_2");
for(int i=0; i< str_vector.size(); i++)
{
std::cout<<str_vector[i]<<std::endl;
}
(2) 请注意resize()与push_back的同时使用,其空间是resize的空间+push_back的空间,否则达不到预设目标.
欢迎大家批评,指正,交流!
联系方式:
emai: tongzhuodenilove@163.com
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