Help Needed!! Marshalling Message

[Terence]

Help Need!!!
I am writing a program for a distributed system course.
I need to marshall all the messages in order to send them thru a socket.
The first 8 bytes of the message are used to store the length of the message,
and then the rest are the actual content of the message.
So I have a big char array, what is the easiest way to store an 8-byte integer
across the first 8 characters in the array?

For Examples:

Integer 1:
00 00 00 00 00 00 00 01 ...

Integer 10:
00 00 00 00 00 00 00 0A ...

Integer 256:
00 00 00 00 00 00 01 00 ...

I don't want to calculate each of the byte
How do I put the integer in this array??


Thanks,

Terence

 

[Thomas Matthews]

Help Need!!!
I am writing a program for a distributed system course.
I need to marshall all the messages in order to send them thru a socket.
The first 8 bytes of the message are used to store the length of the message,
and then the rest are the actual content of the message.
So I have a big char array, what is the easiest way to store an 8-byte integer
across the first 8 characters in the array?

For Examples:

Integer 1:
00 00 00 00 00 00 00 01 ...

Integer 10:
00 00 00 00 00 00 00 0A ...

Integer 256:
00 00 00 00 00 00 01 00 ...

I don't want to calculate each of the byte
How do I put the integer in this array??


Thanks,

Terence

First off, I don't understand what "marshalling" of messages is.
Assuming 8 bits per byte, you need an integer of 64 bits.
Check out "sizeof(long long)" if your compiler supports that type.
Otherwise check your compiler documentation to see if there is
a 64-bit integer.

Try setting a pointer to 64-bit integer to the first location
of the message array. This will only work if the byte-ordering
of the message is the same as the compiler's. If not, you may
have to "load" the integer yourself one byte at a time.

--
Thomas Matthews

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[Frank Schmitt]

Help Need!!!
I am writing a program for a distributed system course.
I need to marshall all the messages in order to send them thru a socket.
The first 8 bytes of the message are used to store the length of the message,
and then the rest are the actual content of the message.
So I have a big char array, what is the easiest way to store an 8-byte
integer across the first 8 characters in the array?

For Examples:

Integer 1:
00 00 00 00 00 00 00 01 ...

Integer 10:
00 00 00 00 00 00 00 0A ...

Integer 256:
00 00 00 00 00 00 01 00 ...

I don't want to calculate each of the byte
How do I put the integer in this array??

The following program shows one way to do it.
Beware: unsigned long long is not a standard c++ type and not
necessarily 64 bits long.

#include <sstream>
#include <string>
#include <iostream>
#include <iomanip>

typedef unsigned long long int64;

std::string marshall(int64 a) {
std:stringstream os;
os << std::setw(8) << std::setfill('0') << std::hex << a;
return os.str();
}

// converts c to hex and fills the first 8 bytes of buf with it
int main() {
int64 c(256);
std::string c_marshalled = marshall(c);
char buf[80] = "xxxxxxxxhello world\n";
std::copy(c_marshalled.begin(),c_marshalled.end(),buf);
std::cout << "buf: " << buf << "\n";
return 0;
}

HTH & kind regards
frank