Redis tutorial (15): C language connection operation code example

In previous blogs, various operating commands, operating mechanisms and server initialization parameter configurations of Redis have been introduced in great detail. This blog is the last in this series of blogs. Here we will give code examples for accessing and operating the Redis server based on the Redis client component. However, it should be noted that since Redis officially does not provide a Windows platform client based on the C interface, the following example can only run on the Linux/Unix platform. But for developers using other programming languages, such as C# and Java, Redis provides client components for these languages. In this way, various interactions with the Redis server based on the Windows platform can also be achieved.

The client used in this blog comes from the Redis official website and is a client component based on the C interface recommended by Redis. See the following link:
https://github.com/antirez/hiredis
In the following code example, the two most commonly used Redis command operation methods are given, namely the ordinary calling method and the pipeline-based calling method.

Note: Please pay attention to the comments when reading the code.

#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <stdarg.h>
#include <string.h>
#include <assert.h>
#include <hiredis.h>
 
void doTest()
{
  int timeout = 10000;
  struct timeval tv;
  tv.tv_sec = timeout / 1000;
  tv.tv_usec = timeout * 1000;
  //以带有超时的方式链接Redis服务器，同时获取与Redis连接的上下文对象。
  //该对象将用于其后所有与Redis操作的函数。
  redisContext* c = redisConnectWithTimeout("192.168.149.137",6379,tv);
  if (c->err) {
    redisFree(c);
    return;
  }
  const char* command1 = "set stest1 value1";
  redisReply* r = (redisReply*)redisCommand(c,command1);
  //需要注意的是，如果返回的对象是NULL，则表示客户端和服务器之间出现严重错误，必须重新链接。
  //这里只是举例说明，简便起见，后面的命令就不再做这样的判断了。
  if (NULL == r) {
    redisFree(c);
    return;
  }
  //不同的Redis命令返回的数据类型不同，在获取之前需要先判断它的实际类型。
  //至于各种命令的返回值信息，可以参考Redis的官方文档，或者查看该系列博客的前几篇
  //有关Redis各种数据类型的博客。:)
  //字符串类型的set命令的返回值的类型是REDIS_REPLY_STATUS，然后只有当返回信息是"OK"
  //时，才表示该命令执行成功。后面的例子以此类推，就不再过多赘述了。
  if (!(r->type == REDIS_REPLY_STATUS && strcasecmp(r->str,"OK") == 0)) {
    printf("Failed to execute command[%s].\n",command1);
    freeReplyObject(r);
    redisFree(c);
    return;
  }
  //由于后面重复使用该变量，所以需要提前释放，否则内存泄漏。
  freeReplyObject(r);
  printf("Succeed to execute command[%s].\n",command1);
 
  const char* command2 = "strlen stest1";
  r = (redisReply*)redisCommand(c,command2);
  if (r->type != REDIS_REPLY_INTEGER) {
    printf("Failed to execute command[%s].\n",command2);
    freeReplyObject(r);
    redisFree(c);
    return;
  }
  int length = r->integer;
  freeReplyObject(r);
  printf("The length of 'stest1' is %d.\n",length);
  printf("Succeed to execute command[%s].\n",command2);
 
  const char* command3 = "get stest1";
  r = (redisReply*)redisCommand(c,command3);
  if (r->type != REDIS_REPLY_STRING) {
    printf("Failed to execute command[%s].\n",command3);
    freeReplyObject(r);
    redisFree(c);
    return;
  }
  printf("The value of 'stest1' is %s.\n",r->str);
  freeReplyObject(r);
  printf("Succeed to execute command[%s].\n",command3);
 
  const char* command4 = "get stest2";
  r = (redisReply*)redisCommand(c,command4);
  //这里需要先说明一下，由于stest2键并不存在，因此Redis会返回空结果，这里只是为了演示。
  if (r->type != REDIS_REPLY_NIL) {
    printf("Failed to execute command[%s].\n",command4);
    freeReplyObject(r);
    redisFree(c);
    return;
  }
  freeReplyObject(r);
  printf("Succeed to execute command[%s].\n",command4);
 
  const char* command5 = "mget stest1 stest2";
  r = (redisReply*)redisCommand(c,command5);
  //不论stest2存在与否，Redis都会给出结果，只是第二个值为nil。
  //由于有多个值返回，因为返回应答的类型是数组类型。
  if (r->type != REDIS_REPLY_ARRAY) {
    printf("Failed to execute command[%s].\n",command5);
    freeReplyObject(r);
    redisFree(c);
    //r->elements表示子元素的数量，不管请求的key是否存在，该值都等于请求是键的数量。
    assert(2 == r->elements);
    return;
  }
  for (int i = 0; i < r->elements; ++i) {
    redisReply* childReply = r->element[i];
    //之前已经介绍过，get命令返回的数据类型是string。
    //对于不存在key的返回值，其类型为REDIS_REPLY_NIL。
    if (childReply->type == REDIS_REPLY_STRING)
      printf("The value is %s.\n",childReply->str);
  }
  //对于每一个子应答，无需使用者单独释放，只需释放最外部的redisReply即可。
  freeReplyObject(r);
  printf("Succeed to execute command[%s].\n",command5);
 
  printf("Begin to test pipeline.\n");
  //该命令只是将待发送的命令写入到上下文对象的输出缓冲区中，直到调用后面的
  //redisGetReply命令才会批量将缓冲区中的命令写出到Redis服务器。这样可以
  //有效的减少客户端与服务器之间的同步等候时间，以及网络IO引起的延迟。
  //至于管线的具体性能优势，可以考虑该系列博客中的管线主题。
  if (REDIS_OK != redisAppendCommand(c,command1)
    || REDIS_OK != redisAppendCommand(c,command2)
    || REDIS_OK != redisAppendCommand(c,command3)
    || REDIS_OK != redisAppendCommand(c,command4)
    || REDIS_OK != redisAppendCommand(c,command5)) {
    redisFree(c);
    return;
  }
 
  redisReply* reply = NULL;
  //对pipeline返回结果的处理方式，和前面代码的处理方式完全一直，这里就不再重复给出了。
  if (REDIS_OK != redisGetReply(c,(void**)&reply)) {
    printf("Failed to execute command[%s] with Pipeline.\n",command1);
    freeReplyObject(reply);
    redisFree(c);
  }
  freeReplyObject(reply);
  printf("Succeed to execute command[%s] with Pipeline.\n",command1);
 
  if (REDIS_OK != redisGetReply(c,(void**)&reply)) {
    printf("Failed to execute command[%s] with Pipeline.\n",command2);
    freeReplyObject(reply);
    redisFree(c);
  }
  freeReplyObject(reply);
  printf("Succeed to execute command[%s] with Pipeline.\n",command2);
 
  if (REDIS_OK != redisGetReply(c,(void**)&reply)) {
    printf("Failed to execute command[%s] with Pipeline.\n",command3);
    freeReplyObject(reply);
    redisFree(c);
  }
  freeReplyObject(reply);
  printf("Succeed to execute command[%s] with Pipeline.\n",command3);
 
  if (REDIS_OK != redisGetReply(c,(void**)&reply)) {
    printf("Failed to execute command[%s] with Pipeline.\n",command4);
    freeReplyObject(reply);
    redisFree(c);
  }
  freeReplyObject(reply);
  printf("Succeed to execute command[%s] with Pipeline.\n",command4);
 
  if (REDIS_OK != redisGetReply(c,(void**)&reply)) {
    printf("Failed to execute command[%s] with Pipeline.\n",command5);
    freeReplyObject(reply);
    redisFree(c);
  }
  freeReplyObject(reply);
  printf("Succeed to execute command[%s] with Pipeline.\n",command5);
  //由于所有通过pipeline提交的命令结果均已为返回，如果此时继续调用redisGetReply，
  //将会导致该函数阻塞并挂起当前线程，直到有新的通过管线提交的命令结果返回。
  //最后不要忘记在退出前释放当前连接的上下文对象。
  redisFree(c);
  return;
}
 
int main() 
{
  doTest();
  return 0;
}
 
//输出结果如下：
//Succeed to execute command[set stest1 value1].
//The length of 'stest1' is 6.
//Succeed to execute command[strlen stest1].
//The value of 'stest1' is value1.
//Succeed to execute command[get stest1].
//Succeed to execute command[get stest2].
//The value is value1.
//Succeed to execute command[mget stest1 stest2].
//Begin to test pipeline.
//Succeed to execute command[set stest1 value1] with Pipeline.
//Succeed to execute command[strlen stest1] with Pipeline.
//Succeed to execute command[get stest1] with Pipeline.
//Succeed to execute command[get stest2] with Pipeline.
//Succeed to execute command[mget stest1 stest2] with Pipeline.

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