How to convert char to int and then display it in hex format

Question

I am making a program in c in which I am getting data from serial device and I am storing it in buffer char receivebuffer[100] . when I display the contents of receivebuffer, the output shows (Is this an ASCII format) . But the expected output is in hex format. How can i convert it in hex?

I also want to know that if I convert buffer to int, will the output be same. Please tell me how can I convert char buffer to int also?

#include <errno.h>
#include <termios.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
int set_interface_attribs (int fd, int speed, int parity)
{
    struct termios tty;
    memset (&tty, 0, sizeof tty);
    if (tcgetattr (fd, &tty) != 0)
    {
            printf("error %d from tcgetattr\n\n", errno);
            printf("Error Opening the device\n\n");
            exit(0);
            //error_message ("error %d from tcgetattr", errno);
            return -1;
    }

    cfsetospeed (&tty, speed);
    cfsetispeed (&tty, speed);

    tty.c_cflag = (tty.c_cflag & ~CSIZE) | CS8;     // 8-bit chars
    // disable IGNBRK for mismatched speed tests; otherwise receive break
    // as \000 chars
    tty.c_iflag &= ~IGNBRK;         // disable break processing
    tty.c_lflag = 0;                // no signaling chars, no echo,
                                    // no canonical processing
    tty.c_oflag = 0;                // no remapping, no delays
    tty.c_cc[VMIN]  = 0;            // read doesn't block
    tty.c_cc[VTIME] = 5;            // 0.5 seconds read timeout

    tty.c_iflag &= ~(IXON | IXOFF | IXANY); // shut off xon/xoff ctrl

    tty.c_cflag |= (CLOCAL | CREAD);// ignore modem controls,
                                    // enable reading
    tty.c_cflag &= ~(PARENB | PARODD);      // shut off parity
    tty.c_cflag |= parity;
    tty.c_cflag &= ~CSTOPB;
    tty.c_cflag &= ~CRTSCTS;

    if (tcsetattr (fd, TCSANOW, &tty) != 0)
    {
            printf("error %d from tcsetattr\n\n", errno);
            printf("Error Opening the device\n\n");
            exit(0);
            //error_message ("error %d from tcsetattr", errno);
            return -1;
    }
    return 0;
}

void set_blocking (int fd, int should_block)
{
    struct termios tty;
    memset (&tty, 0, sizeof tty);
    if (tcgetattr (fd, &tty) != 0)
    {
            printf("error\n\n");
            printf("Error Opening the device\n\n");
                    exit(0);
            //error_message ("error %d from tggetattr", errno);
            return;
    }

    tty.c_cc[VMIN]  = should_block ? 1 : 0;
    tty.c_cc[VTIME] = 5;            // 0.5 seconds read timeout

    if (tcsetattr (fd, TCSANOW, &tty) != 0)
        printf("Error Opening the device\n\n");
        //error_message ("error %d setting term attributes", errno);
}

int main()
{
char *portname = "/dev/ttyUSB0";

int fd = open (portname, O_RDWR | O_NOCTTY | O_SYNC);
if (fd < 0)
{
    //error_message ("error %d opening %s: %s", errno, portname,         strerror (errno));
    printf("error");

}

set_interface_attribs (fd, B9600, 0);  // set speed to 115,200 bps, 8n1 (no parity)
set_blocking (fd, 0);                // set no blocking

       // send 7 character greeting

usleep ((7 + 25) * 100);             // sleep enough to transmit the 7    plus
while(1)
{

char receivebuffer [100];
read (fd, receivebuffer, sizeof receivebuffer);  // read up to 100    characters if ready to read

printf("value of buffer is %s\n\n", receivebuffer);
return 0;
}
}

Answer 1

You should replace this:

printf("value of buffer is %s\n\n", receivebuffer);

with:

for (int tmpfoo = 0; receivebuffer[tmpfoo] != '\0'; tmpfoo++)
{
    printf("value of buffer is %X\n\n", (int)receivebuffer[tmpfoo]);
}

If you want it just to be followed HEXvalue by HEXvalue.

Answer 2

You need to store the count of received bytes somewhere and use that in a for loop try it like this

char receivebuffer[100];
int  count;
int  i;
count = read (fd, receivebuffer, sizeof receivebuffer);  // read up to 100 characters if ready to read
for (i = 0 ; i < count ; ++i)
 {
    printf("0x%02X ", receivebuffer[i]);
    if ((i + 1) % 8 == 0)
        printf("\n");
 }

this if ((i + 1) % 8 == 0) is just to print 8 bytes in a row, you can change or remove it, it helps inspecting the data though.

Answer 3

You don't need to convert it. To display char as a hexadecimal number, use %hhx formatting in printf -group of functions.