1.什么是hiredis
Hiredis 是一个 C 语言编写的 Redis 客户端库，用于与 Redis 数据库进行交互。它提供了一个简洁而高效的接口，使开发人员可以方便地在自己的 C/C++ 项目中使用 Redis。
Hiredis 是一个开源项目，可从其官方 GitHub 仓库获取源代码，并在符合 BSD 许可证的条件下使用和分发。它被广泛应用于各种 C/C++ 项目中，特别是那些需要与 Redis 数据库进行快速、可靠和高性能交互的应用程序。
2.安装hiredis
在centos中可以使用yum直接安装：
yum install hiredis-devel
或者直接从源码安装：
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| git clone https://github.com/redis/hiredis.git
cd hiredis/
make
make install
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3.使用hiredis
使用同步的方式连接redis，只需要使用以下几个函数：
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| redisContext *redisConnect(const char *ip, int port);
void *redisCommand(redisContext *c, const char *format, ...);
void freeReplyObject(void *reply);
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其中，发送指令的函数在使用上与printf类似，支持不定参数：
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| reply = redisCommand(context, "SET foo bar")
reply = redisCommand(context, "SET foo %s", value)
reply = redisCommand(context, "SET key:%s %s", myid, value)
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同时也支持二进制的参数：
reply = redisCommand(context, "SET foo %b", value, (size_t) valuelen);
用%b表示二进制，然后传入二进制value及其长度valuelen
可以封装成一个C++类：
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#include <hiredis/hiredis.h>
#include <iostream>
#include <string>
using namespace std;
class Redis
{
public:
Redis(const char * host, int port = 6379){
c = redisConnect(host, port);
if (c == NULL){
cout << "cannot allocate redis context" << endl;
return;
}
if (c->err){
cout << c->errstr << endl;
c = NULL;
return;
}
}
~Redis(){
if (c){
redisFree(c);
}
}
bool isConnect()
{
return c != NULL;
}
bool Set(const char * key, const char * value)
{
redisReply *reply = (redisReply*) redisCommand(c, "set %s %s", key, value);
if (reply == NULL){
return false;
}
bool success = false;
if (reply->type == REDIS_REPLY_STATUS){
cout << reply->str << endl;
success = true;
} else if (reply->type == REDIS_REPLY_ERROR) {
cout << reply->str << endl;
}
freeReplyObject(reply);
return success;
}
string Get(const char* key)
{
redisReply *reply = (redisReply*) redisCommand(c, "get %s", key);
string value;
if (reply == NULL){
return value;
}
if (reply->type == REDIS_REPLY_STRING){
value = reply->str;
}else if (reply->type == REDIS_REPLY_ERROR){
cout << reply->str << endl;
}
freeReplyObject(reply);
return value;
}
bool HSet(const char * key, const char * field, const char * value)
{
redisReply *reply = (redisReply*) redisCommand(c, "hset %s %s %s", key, field, value);
if (reply == NULL){
return false;
}
bool success = false;
if (reply->type == REDIS_REPLY_STATUS){
cout << reply->str << endl;
success = true;
} else if (reply->type == REDIS_REPLY_ERROR) {
cout << reply->str << endl;
}
freeReplyObject(reply);
return success;
}
string HGet(const char* key, const char * field)
{
redisReply *reply = (redisReply*) redisCommand(c, "hget %s %s", key, field);
string value;
if (reply == NULL){
return value;
}
if (reply->type == REDIS_REPLY_STRING){
value = reply->str;
}else if (reply->type == REDIS_REPLY_ERROR){
cout << reply->str << endl;
}
freeReplyObject(reply);
return value;
}
private:
redisContext *c;
};
int main(){
Redis r("127.0.0.1", 6379);
if (!r.isConnect()){
return 0;
}
r.Set("id", "100");
string value = r.Get("id");
cout << value << endl;
r.HSet("map", "1", "200");
cout << r.HGet("map", "1") << endl;
return 0;
}
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4.hiredis的异步模式
使用hiredis的同步模式时，每一个请求都需要等待回应之后，才能进行下一个请求，时间消耗在IO等待上。为了提高效率，可以使用异步模式，同时发送多个请求，然后回调处理。
使用hiredis的异步模式，需要绑定一个事件适配器，常用的有libevent libuv等。
下面以libevent为例：
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| #include <iostream>
#include <signal.h>
#include <hiredis/async.h>
#include <hiredis/adapters/libevent.h>
struct event_base *eventBase = nullptr;
void signalHandler(int sig, short events, void *arg) {
printf("Received signal %d, exiting...\n", sig);
event_base_loopbreak(eventBase);
}
void commandCallback(redisAsyncContext* context, void* reply, void* data) {
redisReply* r = reinterpret_cast<redisReply*>(reply);
if (r == nullptr) {
std::cout << "Command error: " << context->errstr << std::endl;
return;
}
if (r->type == REDIS_REPLY_ERROR) {
std::cout << "Command error: " << r->str << std::endl;
return;
}
std::cout << r->str << std::endl;
}
void connectCallback(const redisAsyncContext* context, int status) {
if (status == REDIS_OK) {
std::cout << "Connected to Redis" << std::endl;
redisAsyncContext* asyncContext = const_cast<redisAsyncContext*>(context);
redisAsyncCommand(asyncContext, commandCallback, nullptr, "SET mykey Hello");
redisAsyncCommand(asyncContext, commandCallback, nullptr, "GET mykey");
} else {
std::cout << "Connection error" << std::endl;
}
}
int main() {
eventBase = event_base_new();
redisAsyncContext* context = redisAsyncConnect("127.0.0.1", 6379);
if (context->err) {
std::cout << "Connection error: " << context->errstr << std::endl;
return 1;
}
redisLibeventAttach(context, eventBase);
redisAsyncSetConnectCallback(context, connectCallback);
struct event * signalEvent = evsignal_new(eventBase, SIGINT, signalHandler, nullptr);;
evsignal_add(signalEvent, nullptr);
std::cout << "开始事件循环..." << std::endl;
event_base_dispatch(eventBase);
std::cout << "事件循环结束..." << std::endl;
event_free(signalEvent);
event_base_free(eventBase);
redisAsyncDisconnect(context);
return 0;
}
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参考资料