最近开始探索 nanopb - 如果我的问题听起来很愚蠢，请道歉。当我修改 nanopb 的简单示例时，我在分配和检索字符串和整数时遇到了一些问题。让我在我的问题之前给出我的步骤 -
- 我定义了 simple.proto 文件
message Device{
optional string devid =1;
optional string mac = 2;
optional string cpu=3 [default = "x86"] ;
optional bool isSecured=4;
optional int32 uptime = 5 [default = 1234];
}
- 还定义了 simple.option
Device.devid max_size:64
Device.cpu max_size:64
然后我像往常一样编译：protoc -osimple.pb simple.proto
- 这是我的代码：
3a) 使用与如何对 pb_callback_t 类型的字符串进行编码中相同的字符串编码解码实用程序函数
//string encode decode to pb
bool encode_string(pb_ostream_t* stream, const pb_field_t* field, void* const* arg)
{
const char* str = (const char*)(*arg);
if (!pb_encode_tag_for_field(stream, field))
return false;
return pb_encode_string(stream, (uint8_t*)str, strlen(str));
}
bool print_string(pb_istream_t *stream, const pb_field_t *field, void **arg)
{
uint8_t buffer[1024] = {0};
/* We could read block-by-block to avoid the large buffer... */
if (stream->bytes_left > sizeof(buffer) - 1)
return false;
if (!pb_read(stream, buffer, stream->bytes_left))
return false;
/* Print the string, in format comparable with protoc --decode.
* Format comes from the arg defined in main(). */
printf((char*)*arg, buffer);
return true;
}
3b）这是我基于 simple.c 示例的主要代码片段 -
/* This is the buffer where we will store our message. */
uint8_t buffer[128];
size_t message_length;
bool status;
/* Encode our message */
{
/* Allocate space on the stack to store the message data, check out the contents of simple.pb.h
* good to always initialize your structures so that no garbage data from RAM in there. */
//Device message = Device_init_zero; //init zero for empty
Device message = Device_init_default; //init default for default
/* Create a stream that will write to our buffer. */
pb_ostream_t stream = pb_ostream_from_buffer(buffer, sizeof(buffer));
/* Fill in the data */
message.devid.arg = "device1";
message.devid.funcs.encode = &encode_string;
//strcpy(message.devid,"device1"); // no easier way like this ?
message.isSecured = true; // should be 1 if printed with %d
message.uptime=9876; // should change, why it is not working ?
/* Now we are ready to encode the message! */
// encode stream to buffer , also get the buffer length
status = pb_encode(&stream, Device_fields, &message);
message_length = stream.bytes_written;
/* Then just check for any errors.. */
if (!status)
{
printf("Encoding failed: %s\n", PB_GET_ERROR(&stream));
return 1;
}
}
/* Now we could transmit the message over network, store it in a file etc. */
/* just decode it immediately. */
{
/* Allocate space for the decoded message. */
Device message = Device_init_zero;
/* Create a stream that reads from the buffer. */
pb_istream_t stream = pb_istream_from_buffer(buffer, message_length);
message.devid.funcs.decode = &print_string;
message.devid.arg = "before decode Device - devid: %s \n"; //works here
message.cpu.funcs.decode = &print_string;
message.cpu.arg = "before decode Device -cpu: %s \n"; //where in op?
printf("before decode isSecured %d\n",message.isSecured); // doesn't work
printf("before decode uptime %d\n",message.uptime); //doesn't work
/* Now ready to decode the message. */
// decode stream buffer into message
status = pb_decode(&stream, Device_fields, &message);
/* Check for errors... */
if (!status)
{
printf("Decoding failed: %s\n", PB_GET_ERROR(&stream));
return 1;
}
/* Print the data contained in the message. */
message.devid.funcs.decode = &print_string;
message.devid.arg = "after decode Devic - devid: %s \n"; // doesn't work here
printf(" after decode isSecured %d\n",message.isSecured); // prints default 0
printf(" after decode uptime %d\n",(int)message.uptime); //prints default assigned in proto
}
- 构建并运行后的输出：
$ ./simple
before decode isSecured 0
before decode uptime 0
before decode Device - devid: device1
after decode isSecured 0
after decode uptime 1234
我的查询（还在代码中添加了我的内联注释）：
- 在原始 simple.c message.lucky_number=13 分配有效，但这里 message.uptime 分配不起作用，它采用默认值。同样，将布尔值分配给 message.isSecured 也不起作用。请告诉我错在哪里。
- 我在 pb_encode 之前使用了 Device_init_default，因为有些具有默认值，而在 pb_decode 调用之前使用了 Device_init_zero，因为它将在解码后填充。我的方法正确吗？
- 除了 encode_string 和 decode_string util 之外，还有什么更简单的方法可以使用 strcpy 分配字符串值并通过 printf("%s",strvar) 以 C 方式打印它？
- 该字符串仅在 pb_decode 调用之前打印，但正常运行时间默认值在 pb_decode 调用之后打印。布尔值分配也不起作用。为什么 ？我的错误是什么？
- 我在https://github.com/nanopb/nanopb/blob/master/tests/callbacks/encode_callbacks.c中看到了编码字符串和 int 函数 如何编码和解码 float 和 boolean ？
感谢期待