read() -> array

[Tupcia]

This gets char array sent via pipe to a second process and prints it:

int x;
int pipe;
char buf[PIPE_BUF];
while ((x=read(pipe, buf, PIPE_BUF))>0)
    write(fileno(stdout), buf, x);

I want the data to go into 2D array (5x5), so it would look like:

char arr[5][5] = {  'q', 'w', 'e', 'r', 't',
                    'y', 'u', ..............
                     ....
                     ....
                     ...                 'a' };

How can I do this

[nadroj]

have you tried using two for loops?

int x, y;

for ( x = 0; x < 5; x++)
{
  for ( y = 0; y < 5; y++)
  {
     // read character here and assign it to the array at position [x][y]
  }
}

[Tupcia]

int x, y,z;
char arr[5][5];

for ( x = 0; x < 5; x++){
  for ( y = 0; y < 5; y++){
     z=read(pipe, buf, PIPE_BUF);
     arr[x][y] = z;
     printf("%c%c", arr[x][y]);
  }
   printf("\n");
}

This is not working since the elements are not being printed. What is wong ?

[vart]

read function returns number of chars read - so that what you are storing in the array instead of actual buffer read

printf("%c%c", arr[x][y]); - you have 2 format specifiers and only 1 additional argument to the printf - you are asking for crash using it in this way

[matsp]

int x, y,z;
char arr[5][5];

for ( x = 0; x < 5; x++){
  for ( y = 0; y < 5; y++){
     z=read(pipe, buf, PIPE_BUF);  
     // You read into buf, and z contains the number of bytes read. 
     // as a side comment, z is really not a good name here - it implies that it's
     // got something to do with x and y (in a coordinate type way), which is absolutely
     // untrue - perhaps call it "readCount" or "bytesRead" (camel case optional).
     arr[x][y] = z;
     printf("%c%c", arr[x][y]);
     // As pointed out, two format specifications with only one argument will not print the right thing. 
     
  }
   printf("\n");
}

If you read a block of PIPE_BUF size [presuming this is at least 5 * 5 bytes], then you could just loop around and assign arr[x][y] with the corresponding position in buf. If you want to read and immediately assign, you should read one byte at a time [which is definitely not optimal, but may make the logic clearer].

--
Mats