protobuf-c的学习总结

1、前言

项目中用到protobuf-c进行数据序列化，好处在于后期程序扩展性非常好，只需要改动proto的定义就可以保持兼容，非常的灵活方便。关于protobuf-c的详细介绍可以参考google官方文档。https://code.google.com/p/protobuf-c/。在此简单的介绍一下基本功能。proto文件格式如下所示：

message AMessage
{
     requried  int32  a = ;  //a必须出现
     optional  string b = ;  //b是可选的
     repeated  int32  c = ;  //c是数组
}

字段规则类型：

required：表示后面的数据是必须的。

optional：表示后面数据是可选的。

repeated：表示后面的数据是一个数组。

标量数值类型

.proto类型	Java 类型	C++类型	备注
double	double	double
float	float	float
int32	int	int32	使用可变长编码方式。编码负数时不够高效——如果你的字段可能含有负数，那么请使用sint32。
int64	long	int64	使用可变长编码方式。编码负数时不够高效——如果你的字段可能含有负数，那么请使用sint64。
uint32	int[1]	uint32	Uses variable-length encoding.
uint64	long[1]	uint64	Uses variable-length encoding.
sint32	int	int32	使用可变长编码方式。有符号的整型值。编码时比通常的int32高效。
sint64	long	int64	使用可变长编码方式。有符号的整型值。编码时比通常的int64高效。
fixed32	int[1]	uint32	总是4个字节。如果数值总是比总是比228大的话，这个类型会比uint32高效。
fixed64	long[1]	uint64	总是8个字节。如果数值总是比总是比256大的话，这个类型会比uint64高效。
sfixed32	int	int32	总是4个字节。
sfixed64	long	int64	总是8个字节。
bool	boolean	bool
string	String	string	一个字符串必须是UTF-8编码或者7-bit ASCII编码的文本。
bytes	ByteString	string	可能包含任意顺序的字节数据。

2、测试程序

　　编写一个学生信息的proto，proto文件内容如下所示：

 message Student
   {
       required string id = ;
       required string name = ;
       required string gender = ;
       required int32  age = ;
       required string object = ;
       required string home_address = ;
       required string phone = ;
  }

编译命令： protoc-c --c_cout=.  student.proto

生成student.pb-c.c 和 student.pb-c.h两个文件。student.pb-c.h文件内容如下所示：

 /* Generated by the protocol buffer compiler.  DO NOT EDIT! */

 #ifndef PROTOBUF_C_student_2eproto__INCLUDED
 #define PROTOBUF_C_student_2eproto__INCLUDED

 #include <google/protobuf-c/protobuf-c.h>

 PROTOBUF_C_BEGIN_DECLS

 typedef struct _Student Student;

 /* --- enums --- */

 /* --- messages --- */

 struct  _Student
 {
   ProtobufCMessage base;
   char *id;
   char *name;
   char *gender;
   int32_t age;
   char *object;
   char *home_address;
   char *phone;
 };
 #define STUDENT__INIT \
  { PROTOBUF_C_MESSAGE_INIT (&student__descriptor) \
     , NULL, NULL, NULL, , NULL, NULL, NULL }

 /* Student methods */
 void   student__init
                      (Student         *message);
 size_t student__get_packed_size
                      (const Student   *message);
 size_t student__pack
                      (const Student   *message,
                       uint8_t             *out);
 size_t student__pack_to_buffer
                      (const Student   *message,
                       ProtobufCBuffer     *buffer);
 Student *
        student__unpack
                      (ProtobufCAllocator  *allocator,
                       size_t               len,
                       const uint8_t       *data);
 void   student__free_unpacked
                      (Student *message,
                       ProtobufCAllocator *allocator);
 /* --- per-message closures --- */

 typedef void (*Student_Closure)
                  (const Student *message,
                   void *closure_data);

 /* --- services --- */

 /* --- descriptors --- */

 extern const ProtobufCMessageDescriptor student__descriptor;

 PROTOBUF_C_END_DECLS

 #endif  /* PROTOBUF_student_2eproto__INCLUDED */

测试proto程序如下所示：

 #include <stdio.h>
 #include <errno.h>
 #include <stdlib.h>
 #include <string.h>
 #include "student.pb-c.h"

 #define ID_LEN         11
 #define NAME_LEN       32
 #define GENDER_LEN     10
 #define OBJECT_LEN     20
 #define HOME_ADDR_LEN  96
 #define PHONE_LEN      12

 static int malloc_student_info(Student *stu)
 {
     stu->id = (char*)malloc(ID_LEN);
     if (!stu->id)
     {
     goto FAILED;
     }
     stu->name = (char*)malloc(NAME_LEN);
     if (!stu->name)
     {
     goto FAILED;
     }
     stu->gender = (char*)malloc(GENDER_LEN);
     if (!stu->gender)
     {
     goto FAILED;
     }
     stu->object = (char*)malloc(OBJECT_LEN);
     if (!stu->object)
     {
     goto FAILED;
     }
     stu->home_address = (char*)malloc(HOME_ADDR_LEN);
     if (!stu->home_address)
     {
     goto FAILED;
     }
     stu->phone = (char*)malloc(PHONE_LEN);
     if (!stu->phone)
     {
     goto FAILED;
     }
     return ;
 FAILED:
     fprintf(stdout, "malloc error.errno:%u,reason:%s\n",
         errno, strerror(errno));
     return -;
 }

 static void free_student_info(Student *stu)
 {
     if (stu->id)
     {
     free(stu->id);
     stu->id = NULL;
     }
     if (stu->name)
     {
     free(stu->name);
     stu->name = NULL;
     }
     if (stu->gender)
     {
     free(stu->gender);
     stu->gender = NULL;
     }
     if (stu->object)
     {
     free(stu->object);
     stu->object = NULL;
     }
     if (stu->home_address)
     {
     free(stu->home_address);
     stu->home_address = NULL;
     }
     if (stu->phone)
     {
     free(stu->phone);
     stu->phone = NULL;
     }
 }

 static void set_student_info(Student *stu)
 {
     const char *id = "";
     const char *name = "Anker";
     const char *gender = "male";
     const char *object = "computer";
     const char *address = "shen zheng";
     const char *phone = "";

     strncpy(stu->id, id, ID_LEN);
     strncpy(stu->name, name, NAME_LEN);
     strncpy(stu->gender, gender, GENDER_LEN);
     stu->age = ;
     strncpy(stu->object, object, OBJECT_LEN);
     strncpy(stu->home_address, address, HOME_ADDR_LEN);
     strncpy(stu->phone, phone, PHONE_LEN);
 }

 void print_student_info(Student *stu)
 {
     printf("id: %s\n",stu->id);
     printf("name: %s\n",stu->name);
     printf("age: %d\n",stu->age);
     printf("gender:%s\n",stu->gender);
     printf("object: %s\n",stu->object);
     printf("home address: %s\n",stu->home_address);
     printf("phone: %s\n",stu->phone);
 }

 int main()
 {
     Student stu = STUDENT__INIT;
     void *buf = NULL;
     unsigned int len ;
     Student *msg = NULL;

     if (malloc_student_info(&stu) == -) {
         exit();
     }
     set_student_info(&stu);

     //get student packed size
     len = student__get_packed_size(&stu);
     printf("size of student info : %u\n",len);
     buf = malloc(len);
     //put student info pack to buf
     student__pack(&stu, buf);

     //unpack student info from buf
     msg = student__unpack(NULL, len, buf);
     print_student_info(msg);
     //free msg
     student__free_unpacked(msg, NULL);

     free(buf);
     free_student_info(&stu);

     return ;
 }

编译命令： gcc student.pb-c.c main.c -o main -lprotobuf-c

测试结果如下所示：

3、参考网址

http://www.cnblogs.com/dkblog/archive/2012/03/27/2419010.html

https://code.google.com/p/protobuf-c/wiki/Examples