Convert c++ char array to c# string

Question

I have a struct in C++ which has a char[10] field.

struct Package
{
    char str[10];
};

I convert the struct into char array and send it to and c# application over a TCP socket and there I convert it back to a c# struct.

[StructLayout(LayoutKind.Sequential)]
public struct Package
{
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 10)]
    public string str;
};

The convertion is done properly and I get the message but the problem is when the length of the message is less than the size of the array and I think that it's due to the null terminator in c++ char array.

For instance if the I send "Hello\0" from C++ the char array is something like:

H e l l o \0 \0 \0 \0 \0

And when I get it in c# application it is something like:

H e l l o Ì Ì Ì Ì Ì

And I really don't know what to do with this (personally like to call) junk character 'Ì'.

please help me on this. Any help is appreciated.

Update:

I simply cast the struct to char* and send it over the socket;

Package pkg;
strcpy_s(pkg.str, 'Hello\0');

char* bytes = (char*)&pkg;

send(socket, bytes, sizeof(pkg), NULL);

Your array size is 10. Try type 10 characters. You don't have this character 'Ì'.So you can split string. This is one solution. — Nejc Galof
– Nejc Galof, Commented Dec 20, 2014 at 9:03
Your solution is good for 10 character but what if I need to have more and more characters. Howerver your answer reminded me of that I can have an end of the string character when I send the char array from c++. Still I'm waiting for more helps. — user3530012
– user3530012, Commented Dec 20, 2014 at 9:06
It seems that in c# code you doesn't receive '\0' char. Or is never sent to you in C++, but in c++ the array is set "memsetted" to 0x00 for all chars by default — LPs
– LPs, Commented Dec 20, 2014 at 9:08
Actually even if I put '\0' at the end of the char array in C++ it never receives in c#. — user3530012
– user3530012, Commented Dec 20, 2014 at 9:09
I thnk we need more code. Paste the way you use to pass from C++ array to C# string — LPs
– LPs, Commented Dec 20, 2014 at 9:11

Iharob Al Asimi · Accepted Answer · 2014-12-20 09:42:19Z

4

I don't know any C#, but may be you can solve the problem this way

Package pkg;
strcpy_s(pkg.str, 10, "Hello");

char* bytes = (char*)&pkg;

send(socket, bytes, sizeof(pkg), NULL);

The strcpy_s function takes the size of the dst buffer as an argument to avoid an overflow (see here). I asked in the comments about the way you inovke it, because it doesn't even look like it's valid C++.

The terminating null byte is added to pkg.str automatically and also "Hello" has a terminating null byte after the o character, and you don't have to add it manually.

I assumed that C# knows how to handle the recieved string, so if you send the right string, it should be recived correctly.

edited Dec 20, 2014 at 9:42

answered Dec 20, 2014 at 9:32

Iharob Al Asimi

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2 Comments

user3530012 Over a year ago

It amazingly worked. I don't know why you received a negative vote. Anyway what is the explanation?

Iharob Al Asimi Over a year ago

BTW: sizeof(pkg) is perfectly ok as long as pkg.str is an array and not a pointer, if it is a pointer, then it would be sizeof(pkg) + strlen(pkg.str) + 1, the + 1 for the terminating null byte. And you wold have to allocate space for the string using malloc.

LPs · Accepted Answer · 2014-12-20 09:24:51Z

2

You are sending sizeof array instead of strlen of str.

Take notes that if you send with strlen you need to add 1 to send the null termination of string

answered Dec 20, 2014 at 9:24

LPs

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Comments

LPs · Accepted Answer · 2014-12-20 09:19:19Z

1

This is what I usually do in my wrappers dll with serial line

        public byte[] RXArray = new byte[length];

        byte[] appo = new byte[MsgLength];
        Array.ConstrainedCopy(RXArray, NcharsToCopy, appo, 0, MsgLength);
        string ConvertedToString = System.Text.Encoding.UTF8.GetString(appo);

answered Dec 20, 2014 at 9:19

LPs

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