Interpreting received "Data" object in cpp

Question

harshal_goyal OP

Created Sep ’24

Replies 3

Boosts 0

Participants 2

Hello Everyone,

I have a use case where I wanted to interpret the "Data" object received as a part of my NWConnection's recv call. I have my interpretation logic in cpp so in swift I extract the pointer to the raw bytes from Data and pass it to cpp as a UnsafeMutableRawPointer.

In cpp it is received as a void * where I typecast it to char * to read data byte by byte before framing a response.

I am able to get the pointer of the bytes by using

// Swift Code

// pContent is the received Data 

if let content = pContent, !content.isEmpty {

    bytes = content.withUnsafeBytes { rawBufferPointer in

        guard let buffer = rawBufferPointer.baseAddress else {

                 // return with null data. 
        }
         // invoke cpp method to interpret data and trigger response.
    }

// Cpp Code


void InterpretResponse (void * pDataPointer, int pDataLength) {

    char * data = (char *) pDataPointer;
    for (int iterator = 0; iterator < pDataLength; ++iterator ) 
      {
        std::cout << data<< std::endl;
        data++;
      }
}

When I pass this buffer to cpp, I am unable to interpret it properly. Can someone help me out here?

Thanks :)

Harshal

Answered by DTS Engineer in 806991022

That was also posted by me.

Sure. But if you’re gonna ‘forums surf’, it’s only polite to link to your other attempts.

Anyway, with regards your code, I think this is a simply a case of a missing *. Consider these two C++ files:

Test.hpp:

#ifndef Test_hpp
#define Test_hpp

#include <cstddef>

extern void qqqTest(const void * base, size_t len);

#endif /* Test_hpp */

Test.cpp:

#include "Test.hpp"

#include <iostream>

extern void qqqTest(const void *base, std::size_t len) {
    const char * cursor = (const char *) base;
    for (size_t i = 0; i < len; i++) {
        std::cout << *cursor << std::endl;
        cursor++;
    }
}

and this Swift file:

main.swift:

import Foundation

func main() {
    let d = Data("Hello Cruel World!".utf8)
    d.withUnsafeBytes { buf in
        qqqTest(buf.baseAddress!, buf.count)
    }    
}

main()

If I put them all into a command-line tool target and run it on my Mac (Xcode 16.0 on macOS 14.6.1), I got this:

H
e
l
l
o
 
C
r
u
e
l
 
W
o
r
l
d
!

Note that I’m using *cursor in the place where your code has just data.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

Boost

Answer 1

DTS Engineer OP

Apple

Oct ’24

link

0

Answer 2

harshal_goyal OP

Oct ’24

Hi @DTS Engineer ,

That was also posted by me. There was another thread which is not identical but had some similar case of interpreting Data in cpp , although it was an attempt with std::vector. (link)

Could you help out on how can this be achieved?

Thanks :)

Harshal

0

Answer 3

DTS Engineer OP

Apple

Oct ’24

Accepted Answer

Recommended

That was also posted by me.

Sure. But if you’re gonna ‘forums surf’, it’s only polite to link to your other attempts.

Anyway, with regards your code, I think this is a simply a case of a missing *. Consider these two C++ files:

Test.hpp:

#ifndef Test_hpp
#define Test_hpp

#include <cstddef>

extern void qqqTest(const void * base, size_t len);

#endif /* Test_hpp */

Test.cpp:

#include "Test.hpp"

#include <iostream>

extern void qqqTest(const void *base, std::size_t len) {
    const char * cursor = (const char *) base;
    for (size_t i = 0; i < len; i++) {
        std::cout << *cursor << std::endl;
        cursor++;
    }
}

and this Swift file:

main.swift:

import Foundation

func main() {
    let d = Data("Hello Cruel World!".utf8)
    d.withUnsafeBytes { buf in
        qqqTest(buf.baseAddress!, buf.count)
    }    
}

main()

If I put them all into a command-line tool target and run it on my Mac (Xcode 16.0 on macOS 14.6.1), I got this:

H
e
l
l
o
 
C
r
u
e
l
 
W
o
r
l
d
!

Note that I’m using *cursor in the place where your code has just data.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

1