Linux包含hash_map和hash_set的not declared问题

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当在Linux下cpp文件包含hash_map或hash_set时，会出现"‘hash_map’ was not declared in this scope"问题。

#include <iostream>#include <string>#include <hash_map>using namespace std;int main(void){hash_map<int, string> hmap;hmap[1] = "hi hdu1";hmap[2] = "hi hdu2";hmap[3] = "hi hdu3";hash_map<int, string>::iterator iter;iter = hmap.find(2);if (iter != hmap.end()){cout << iter->second << endl;}else{cout << "not find" << endl;}return 0;}

原因：hash_map是声明在__gnu_cxx命名空间的，所以只要在程序中添加using namespace __gnc_cxx就可以了^_^

#include <iostream>#include <string>#include <hash_map>using namespace std;using namespace __gnu_cxx;int main(void){hash_map<int, string> hmap;hmap[1] = "hi hdu1";hmap[2] = "hi hdu2";hmap[3] = "hi hdu3";hash_map<int, string>::iterator iter;iter = hmap.find(2);if (iter != hmap.end()){cout << iter->second << endl;}else{cout << "not find" << endl;}return 0;}

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