How to send unsigned char over tcp ?

Question

4.00/5 (1 vote)

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i need help to send unsigned character over tcp in unix
but it case error in this line

C++

void Write(char * a,int size)
{
  unsigned char dt []=a;// erorr
  write(Socket,a,2); // error
 
}

Posted 26-Oct-14 4:32am

Mahmoud_Gamal

Updated 21-Jun-15 21:50pm

v5

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Comments

[no name] 26-Oct-14 10:38am

Do you really think tcp does bother about data types?

Mahmoud_Gamal 27-Oct-14 4:02am

not tcp but the data in accept in write function

CPallini 26-Oct-14 10:43am

Provided Socket is a file descriptor (that is a int) the line
write(Socket, dt, 2);
should compile fine. What is the exact error message you are getting?

Mahmoud_Gamal 27-Oct-14 4:31am

it compile fine but i need to send unsigned char
i will update question
sorry for this

CPallini 27-Oct-14 10:11am

unsigned char dt []=a;
Is of course wrong. What are trying to do?

Mahmoud_Gamal 27-Oct-14 17:31pm

i know it wrong it just dummy code i want to cast

4 solutions

Solution 2

Internally, a signed and an unsigned type are the same. The char you send is just 8 bits of data, just like an unsigned char. Therefore,

C

void Write(char * arr,int size)
{
  unsigned char* dt = (unsigned char*)a; // Cast to the type you want
  write(Socket,dt,size);
}

will send exactly the same data as

C

void Write(char * arr,int size)
{
  write(Socket,arr,size);
}

Posted 27-Oct-14 1:30am

Orjan Westin

Comments

Mahmoud_Gamal 23-Jun-15 3:50am

but i see unlike when i send data in range unsigned not signed and i receive wrong data i do like your solution but doesn't work well

Solution 3

i solve it temporary like this

C++

void WriteU(unsigned   char buff[], int size)
{
    int h ;

        h = write( m_Client->Socket,buff,size);
//          printf("\n data write \n %i",h);

}

why i tired my self if there is another way

Posted 27-Oct-14 11:35am

Mahmoud_Gamal

Solution 4

Your Write function takes a character pointer as input, so trying to use that as an unsigned pointer makes no sense. You should just use the standard socket write function as described in http://man7.org/linux/man-pages/man2/write.2.html[^].

Posted 21-Jun-15 22:38pm

Richard MacCutchan

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Jochen Arndt · Accepted Answer · 2014-10-27T00:06:00

Just pass the file descriptor, arr and size to the write function. The type of the buffer pointer does not care as far as the count parameter specifies a valid number of bytes contained in the buffer. See also man 2 write[^].

The write function just transfers data. It does not care what kind of data are transferred. For that reason the type of the second parameter is void *.