Member Avatar for yuvaraj.tr

Hi ,

I have one buffer size is 50 bytes and reading 50 byte data from file

unsigned char bufffer[50];

read(fd,buffer,50); // Consider each byte numerical is value is zero.

printf("@@%s@@",buffer); // Here i will get @@@@ only.

But I want @@(50 zero)@@ as output(i have to use %c or %s only). If 25th byte numerical value is zero. It will print only 25 bytes only but i want print entire buffer if it has null terminal(ZERO) middle of the buffer also)

Any help !!

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  • Latest Post Latest Post by jephthah

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The core issue is that the buffer you read is raw/binary data, not a C string, so any string-format printing will stop at the first NUL byte. As pointed out, treat the data as binary; as showed, examining each byte is the common fix. Two quick safety notes before proceeding: always use the return value from read() to know how many bytes you actually received, and if you intend to use string APIs make room for a terminating NUL to avoid undefined behavior (read(2) man page, printf(3) man page).

Practical choices (pick based on desired visible output):

  • Send raw bytes unchanged to an output sink that accepts binary (use write/fwrite with the exact byte count). NULs will be transmitted but are invisible on a terminal.
  • If every zero byte must appear visibly (for example as the character '0' or an escape like "[00]"), create a separate printable buffer: allocate enough space, map each input byte to either its printable form or your chosen marker, terminate that buffer, then print it as a string. This lets you still call printf once while avoiding mid-buffer NULs.
  • For full safety and clarity, produce a hex/escaped dump (or use hexdump/xxd) so control characters cannot disturb the terminal.

Cautions: printing raw binary can trigger control characters (backspace, BEL, cursor moves). Use isprint()/classification or hex escapes when you need predictable, portable output.

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Member Avatar for Ancient Dragon

One way to do it is to print each byte one at a time in a loop. %s is for null terminated strings. What you apparently have is a binary file, not a text file. There is no standard C function that will print that entire buffer the way you want it.

Member Avatar for jephthah 
char buffer[BUFF_SIZE];

printf("string [");

for (i=0; i<BUFF_SIZE; i++)
{
    if (buffer[i] == '\0')
        printf("0");

    else
        printf("%c",buffer[i]);
}

printf("]\n");
Edited by jephthah because: n/a
Member Avatar for jephthah

there are more clever ways to do it but that gives you an idea

Edited by jephthah because: double post, oops.
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