protobuf的C简单的代码例子（一）

根据语言指导手册创建一个简单的文件：amessage.proto ，内容如下

message
AMessage

{

required int32 a=1;

optional int32 b=2;

}
t通过命令行产生相应的.h和.c源文件。 # protoc-c
--c_out=. amessage.proto

C文件如下所示
#include<stdio.h>

#include<stdlib.h>

#include"amessage.pb-c.h"

int main
(int argc,constchar*
argv[])

{

AMessage msg
= AMESSAGE__INIT;// AMessage

void*buf;
// Buffer to storeserialized data

unsigned len;
// Length of serialized data

if(argc
!=2&& argc
!=3)

{
// Allow one or twointegers

fprintf(stderr,"usage:amessage
a [b]\n");

return1;

}

msg.a
= atoi(argv[1]);

if(argc
==3){
msg.has_b
=1; msg.b
= atoi(argv[2]);}

len =amessage__get_packed_size(&msg);

buf = malloc(len);

amessage__pack(&msg,buf);

fprintf(stderr,"Writing
%dserialized bytes\n",len);// See the lengthof message

fwrite(buf,len,1,stdout);//
Write to stdoutto allow direct command line piping

free(buf);//
Free theallocated serialized buffer

return0;

}
注意以下几点:

使用A_MESSAGE__INIT宏创建信息的架构
参数b是可选的

amessage__get_packed_size返回数据包的长度。

a_message__pack 对你设计的信息进行打包。

下面给出对amessage解包的代码。

#include<stdio.h>

#include<stdlib.h>

#include"amessage.pb-c.h"

#define MAX_MSG_SIZE
1024

static size_t

read_buffer (unsigned max_length,
uint8_t *out)

{

size_t cur_len =0;

uint8_t c;

while((nread=fread(out+
cur_len,1, max_length
- cur_len, stdin))!=0)

{

cur_len += nread;

if(cur_len
== max_length)

{

fprintf(stderr,"max
messagelength exceeded\n");

exit(1);

}

}

return cur_len;

}

int main
(int argc,constchar*
argv[])

{

AMessage*msg;

// Read packed message from standard-input.

uint8_t buf[MAX_MSG_SIZE];

size_t msg_len = read_buffer
(MAX_MSG_SIZE, buf);

// Unpack the message using protobuf-c.

msg = amessage__unpack(NULL,
msg_len, buf);

if(msg
== NULL)

{

fprintf(stderr,"errorunpacking
incoming message\n");

exit(1);

}

// display the message's fields.

printf("Received: a=%d",msg->a);
// required field

if(msg->has_b)
// handle optionalfield

printf(" b=%d",msg->b);

printf("\n");

// Free the unpacked message

amessage__free_unpacked(msg,
NULL);

return0;

}
编译连接的时候要包含 '-lprotobuf-c'，否则编译不通过
Test by piping one program into the next atcommand line:
#./amessage_serialize
10 2
| ./amessage_deserialize
---->使用管道命令

Writing:4 serialized bytes

Received: a=10
b=2