\u5728 C++ \u7684 std::map \u4e2d，\u65e0\u8bba\u662f insert \u8fd8\u662f emplace，\u5f53 key \u5df2\u7ecf\u5b58\u5728\u65f6\u90fd\u4e0d\u4f1a\u8986\u76d6\u539f\u6709\u7684\u503c\u3002\u4e24\u8005\u90fd\u9075\u5faa\u201c\u53ea\u63d2\u5165\u3001\u4e0d\u66f4\u65b0\u201d\u7684\u8bed\u4e49：\u5982\u679c\u5bb9\u5668\u4e2d\u5df2\u7ecf\u5b58\u5728\u7b49\u4ef7 key，\u63d2\u5165\u64cd\u4f5c\u76f4\u63a5\u5931\u8d25（\u6216\u4ec0\u4e48\u90fd\u4e0d\u505a），\u539f\u6709 value \u4fdd\u6301\u4e0d\u53d8\u3002<\/p>\n
\u771f\u6b63\u4f1a\u8986\u76d6\u5df2\u6709\u503c\u7684\u662f operator[] \u548c insert_or_assign\u3002\u8fd9\u662f\u5f88\u591a\u521d\u5b66\u8005\u5bb9\u6613\u6df7\u6dc6\u7684\u5730\u65b9\u3002<\/p>\n
insert \u7684\u8fd4\u56de\u503c\u662f\u4e00\u4e2a pair<iterator, bool>，\u5176\u4e2d bool \u8868\u793a\u662f\u5426\u63d2\u5165\u6210\u529f\u3002key \u5df2\u5b58\u5728\u65f6\u8fd4\u56de false，\u8fed\u4ee3\u5668\u6307\u5411\u5df2\u5b58\u5728\u7684\u90a3\u4e2a\u5143\u7d20，\u503c\u4e0d\u4f1a\u88ab\u4fee\u6539\u3002<\/p>\n
#include <iostream>
\n#include <map>
\n#include <string><\/p>\n
int main() {
\n std::map<std::string, int> m;
\n m.insert({"apple", 1});<\/p>\n
auto ret = m.insert({"apple", 100});
\n std::cout << "inserted: " << ret.second << "\\\\n"; \/\/ 0
\n std::cout << "value: " << m["apple"] << "\\\\n"; \/\/ 1，\u672a\u88ab\u8986\u76d6
\n return 0;
\n}<\/p>\n
\u53ef\u4ee5\u770b\u5230，\u7b2c\u4e8c\u6b21\u63d2\u5165\u7684 100 \u88ab\u76f4\u63a5\u4e22\u5f03，m["apple"] \u4ecd\u7136\u662f 1\u3002<\/p>\n
emplace \u540c\u6837\u662f\u201c\u53ea\u5728 key \u4e0d\u5b58\u5728\u65f6\u6784\u9020\u5e76\u63d2\u5165\u201d\u3002\u5b83\u7684\u8fd4\u56de\u503c\u4e0e insert \u4e00\u81f4，\u4e5f\u662f pair<iterator, bool>\u3002key \u5df2\u5b58\u5728\u65f6\u8fd4\u56de false，\u5e76\u4e14\u4e0d\u4f1a\u7528\u65b0\u53c2\u6570\u53bb\u8986\u76d6\u65e7\u503c\u3002<\/p>\n
#include <iostream>
\n#include <map>
\n#include <string><\/p>\n
int main() {
\n std::map<std::string, int> m;
\n m.emplace("apple", 1);<\/p>\n
auto ret = m.emplace("apple", 100);
\n std::cout << "inserted: " << ret.second << "\\\\n"; \/\/ 0
\n std::cout << "value: " << m["apple"] << "\\\\n"; \/\/ 1，\u672a\u88ab\u8986\u76d6
\n return 0;
\n}<\/p>\n
\u4e24\u8005\u5728\u201c\u662f\u5426\u8986\u76d6\u201d\u8fd9\u4e00\u70b9\u4e0a\u6ca1\u6709\u533a\u522b，\u771f\u6b63\u7684\u5dee\u5f02\u5728\u4e8e\u6784\u9020\u65f6\u673a\u548c\u53c2\u6570\u4f20\u9012\u65b9\u5f0f：<\/p>\n
\u4f46\u8981\u6ce8\u610f：emplace \u5e76\u4e0d\u4fdd\u8bc1\u4e00\u5b9a\u6bd4 insert \u5feb\u3002\u5982\u679c key \u5df2\u5b58\u5728，emplace \u4ecd\u7136\u53ef\u80fd\u5148\u6784\u9020\u51fa\u4e34\u65f6\u5bf9\u8c61\u518d\u53d1\u73b0\u91cd\u590d\u800c\u4e22\u5f03，\u6b64\u65f6\u53cd\u800c\u53ef\u80fd\u6bd4 insert \u591a\u505a\u4e00\u6b21\u6784\u9020\u3002\u56e0\u6b64\u4e0d\u80fd\u76f2\u76ee\u8ba4\u4e3a emplace \u603b\u662f\u66f4\u4f18\u3002<\/p>\n
\u5982\u679c\u786e\u5b9e\u5e0c\u671b\u5728 key \u5b58\u5728\u65f6\u66f4\u65b0\u503c，\u5e94\u8be5\u4f7f\u7528\u4e0b\u9762\u4e24\u79cd\u65b9\u5f0f：<\/p>\n
#include <iostream>
\n#include <map>
\n#include <string><\/p>\n
int main() {
\n std::map<std::string, int> m;
\n m["apple"] = 1;<\/p>\n
\/\/ \u65b9\u5f0f\u4e00：operator[]，key \u4e0d\u5b58\u5728\u4f1a\u9ed8\u8ba4\u6784\u9020，\u5b58\u5728\u5219\u8986\u76d6
\n m["apple"] = 100;
\n std::cout << m["apple"] << "\\\\n"; \/\/ 100<\/p>\n
\/\/ \u65b9\u5f0f\u4e8c：insert_or_assign（C++17），\u8bed\u4e49\u66f4\u660e\u786e
\n m.insert_or_assign("apple", 200);
\n std::cout << m["apple"] << "\\\\n"; \/\/ 200
\n return 0;
\n}<\/p>\n
\u4e24\u8005\u7684\u533a\u522b\u5728\u4e8e：operator[] \u5728 key \u4e0d\u5b58\u5728\u65f6\u4f1a\u5148\u9ed8\u8ba4\u6784\u9020\u4e00\u4e2a value，\u8981\u6c42 T \u53ef\u9ed8\u8ba4\u6784\u9020；\u800c insert_or_assign \u4e0d\u5b58\u5728\u65f6\u76f4\u63a5\u63d2\u5165，\u4e0d\u8981\u6c42\u9ed8\u8ba4\u6784\u9020，\u8bed\u4e49\u4e5f\u66f4\u6e05\u6670\u3002<\/p>\n
| insert<\/td>\n | \u4e0d\u63d2\u5165，\u4e0d\u8986\u76d6<\/td>\n | pair<iterator, bool><\/td>\n<\/tr>\n |
| emplace<\/td>\n | \u4e0d\u63d2\u5165，\u4e0d\u8986\u76d6<\/td>\n | pair<iterator, bool><\/td>\n<\/tr>\n |
| operator[]<\/td>\n | \u8986\u76d6（\u4e0d\u5b58\u5728\u5219\u9ed8\u8ba4\u6784\u9020）<\/td>\n | \u503c\u7684\u5f15\u7528<\/td>\n<\/tr>\n |
| insert_or_assign<\/td>\n | \u8986\u76d6（\u4e0d\u5b58\u5728\u5219\u63d2\u5165）<\/td>\n | pair<iterator, bool><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \u4e00\u53e5\u8bdd\u8bb0\u5fc6：insert \u548c emplace \u90fd\u662f\u201c\u63d2\u5165\u201d，\u4e0d\u662f\u201c\u8d4b\u503c\u201d；\u8981\u8986\u76d6\u8bf7\u7528 operator[] \u6216 insert_or_assign\u3002<\/p>\n","protected":false},"excerpt":{"rendered":" \u5148\u8bf4\u7ed3\u8bba\u5728 C \u7684 std::map \u4e2d，\u65e0\u8bba\u662f insert \u8fd8\u662f emplace，\u5f53 key \u5df2\u7ecf\u5b58\u5728\u65f6\u90fd\u4e0d\u4f1a\u8986\u76d6\u539f\u6709\u7684\u503c\u3002\u4e24\u8005\u90fd\u9075\u5faa\u201c\u53ea\u63d2\u5165\u3001\u4e0d\u66f4\u65b0\u201d\u7684\u8bed\u4e49：\u5982\u679c\u5bb9\u5668\u4e2d\u5df2\u7ecf\u5b58\u5728\u7b49\u4ef7 key，\u63d2\u5165\u64cd\u4f5c\u76f4\u63a5\u5931\u8d25（\u6216\u4ec0\u4e48\u90fd\u4e0d\u505a），\u539f\u6709 value \u4fdd\u6301\u4e0d\u53d8\u3002\u771f\u6b63\u4f1a\u8986\u76d6\u5df2\u6709\u503c\u7684\u662f operator[] \u548c insert_or_assign\u3002\u8fd9\u662f\u5f88\u591a\u521d\u5b66\u8005\u5bb9\u6613\u6df7\u6dc6\u7684\u5730\u65b9\u3002insert<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[55,4233,190,1813,427],"topic":[],"class_list":["post-123870","post","type-post","status-publish","format-standard","hentry","category-server","tag-c","tag-map","tag-190","tag-1813","tag-427"],"yoast_head":"\n |