I have std::stringstream with 1 byte:
std::stringstream message;
message.write((const char[]) {0x55}, 1);
std::string res(message.str());
How append int a = 1; (4 bytes)?
I want to get as values stored in the message's underlying std::string:
0x55 0x00 0x00 0x00 0x01
And right tool I chose for the job with the sequence of bytes?
"How append
int a = 1;(4 bytes)?"
Simply like that:
uint32_t a = 1; // Use uint32_t to be sure to have 4 bytes.
message.write((const char*)&a, sizeof(a));
As you mention "specific socket protocol", you'll probably need to take care of the network byte order using the htonl() function:
uint32_t a = htonl(1);
Writing an int might differ based on internal byte order, big endian, little endian, or others.
It would be more portable to mask off each byte logically, and then put each unsigned char into the stream
You will need to rebuild the int on the recieving side, again using logical operations like shift
It is also likely you will not need all 4 bytes, so you could easily just send 3 for example.
You should look up shifting and masking and understand them if you plan to do binary streams.
The following will do, with function Append4ByteInteger doing the actual work:
#include <iostream>
#include <sstream>
#include <string>
static std::stringstream& Append4ByteInteger (std::stringstream& stream, int value) {
auto v = static_cast<uint32_t>(value);
stream << static_cast<unsigned char>(v >> 24);
stream << static_cast<unsigned char>(v >> 16);
stream << static_cast<unsigned char>(v >> 8);
stream << static_cast<unsigned char>(v);
return stream;
}
int main () {
std::stringstream message;
message.write((const char[]) {0x55}, 1);
Append4ByteInteger(message, 1);
std::cout << "result: '" << message.str() << "'" << std::endl;
}
You can check that the stream actually contains 0x00 0x00 0x00 0x01 using a hex dump utility (e.g. hexdump).
Note that the function assumes that the integer has a value of 0 or greater. If you want to ensure that, you may want to use an unsigned int instead, or probably even a uint32_t, as the size of an int is platform-dependent.
0x55 0x00 0x00 0x00 0x01? Are you sure you want to treat it as a byte buffer instead of a textual string? Just asking to make surestd::stringis notstd::stringstream, finding out how to usestd::stringstreamis easy, and your syntax is made-up. Which book are you using?std::string? The code you've shown is not valid C++, it's using C's compound literals which your compiler allows as an extension.