tr1 的 unorderd_map

Thu, 24 Apr 2014 11:17:15 +0800

#include <tr1/unordered_map>
#include <stdio.h>
#include <string>

int main() {
    typedef std::tr1::unordered_map<std::string, int> HashMap;
    HashMap mapNumber;
    mapNumber["one"] = 1;
    mapNumber["two"] = 2;
    std::tr1::hash<std::string> hashFunc = mapNumber.hash_function();
    for (HashMap::const_iterator it = mapNumber.begin();
            it != mapNumber.end(); it++) {
        printf("%s(hash code: %d) -> %d\n", it->first.c_str(),
                hashFunc(it->first), it->second);
    }
    return 0;
}

two(hash code: 1149015817) -> 2
one(hash code: 566910127) -> 1

如果需要自定义类型，可以看这里，http://hi.baidu.com/wewe39/item/c342d5f48cb25d0ec6dc45a9

稍后做一下和 std::map 的查找效率对比

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2014-4-24 13:03:39 update

刚刚看了一下效率对比

#include <tr1/unordered_map>
#include <map>
#include <stdio.h>
#include <string>
#include <sys/time.h>
#include <time.h>
#include <stdlib.h>

std::map<std::string, int> rbtreeMap;
std::tr1::unordered_map<std::string, int> hashMap;

void printtime() {
    struct timeval tm;
    gettimeofday(&tm, NULL);
    printf("%lu, %lu\n", tm.tv_sec, tm.tv_usec);
}

void initRbtreeMap(int init_count) {
    for (int i = 0; i < init_count; i++) {
        int r = rand() % init_count;
        char str[16] = {0};
        snprintf(str, sizeof str, "%d", r);
        rbtreeMap[str] = r;
    }
    printf("rb tree map size %d\n", rbtreeMap.size());
}

void initHashMap(int init_count) {
    for (int i = 0; i < init_count; i++) {
        int r = rand() % init_count;
        char str[16] = {0};
        snprintf(str, sizeof str, "%d", r);
        hashMap[str] = r;
    }
    printf("hash map size %d\n", hashMap.size());
}

void testRbtreeMap(int init_count, int test_count) {
    int hit = 0, miss = 0;
    for (int i = 0; i < test_count; i++) {
        int r = rand() % init_count;
        char str[16] = {0};
        snprintf(str, sizeof str, "%d", r);
        if (rbtreeMap.find(str) == rbtreeMap.end()) {
            miss++;
        } else {
            hit++;
        }
    }
    printf("rb tree hit count %d miss count %d\n",
            hit, miss);
}

void testHashMap(int init_count, int test_count) {
    int hit = 0, miss = 0;
    for (int i = 0; i < test_count; i++) {
        int r = rand() % init_count;
        char str[16] = {0};
        snprintf(str, sizeof str, "%d", r);
        if (hashMap.find(str) == hashMap.end()) {
            miss++;
        } else {
            hit++;
        }
    }
    printf("hash tree hit count %d miss count %d\n",
            hit, miss);
}

int main() {
    srand(time(NULL));
    int init_count = 500 * 1000;
    printtime();
    initRbtreeMap(init_count);
    printtime();
    initHashMap(init_count);
    printtime();
    int test_count = 10 * 1000 * 1000;
    testRbtreeMap(init_count, test_count);
    printtime();
    testHashMap(init_count, test_count);
    printtime();
    return 0;
}

1398315723, 65363
rb tree map size 316072
1398315724, 33265
hash map size 316202
1398315724, 423226
rb tree hit count 6320750 miss count 3679250
1398315743, 283560
hash tree hit count 6323107 miss count 3676893
1398315748, 386742

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tr1 的 unorderd_map