How to extract number from a string correctly?

Janet · #1 (**permalink**) March 7th, 2004, 12:15 PM

hi,

I wish to extract 9 and 46 from a string
"PORT 10,247,56,67,9,46\r\n"
, where \r is 0x0D and \n 0x0A

Note that the string is not ended with \0, so the string length is 24 bytes.
Note that also the number of bytes for each number is not fixed,
for example, "PORT 101,247,56,67,9,46\r\n" could be 25 bytes in length.

However, the maximum of each number is 255, which is FF in hex.

the 9 and 46 is a port number, which is 2350.
9 = 0x09, 46 = 0x2E;

2350 == 0x09 2E

In short, the function will return 0x092E.
I use str

to ease you to test the code, I paste the code i typed here,
This function will not work because *string_ptr only returns one byte.

int8 FTPGetRemotePort(BYTE *buffer) {
BYTE *string_ptr;
BYTE deliminator[] = "PORT ,\r\n";
BYTE i;
BYTE high_byte;
BYTE low_byte;

string_ptr = strtok(buffer, deliminator);

for (i = 0; i < 6; i++) {
string_ptr = strtok(NULL, deliminator);

if (i == 4) {
high_byte = *string_ptr;
}

if (i == 5) {
low_byte = *string_ptr;
}
}
return make16(high_byte, low_byte);
}
BYTE buffer[40];

buffer[0] = 0x50;
buffer[1] = 0x4f;
buffer[2] = 0x52;
buffer[3] = 0x54;
buffer[4] = 0x20;
buffer[5] = 0x31;
buffer[6] = 0x30;
buffer[7] = 0x2c;
buffer

= 0x32;
buffer[9] = 0x34;
buffer[10] = 0x37;
buffer[11] = 0x2c;
buffer[12] = 0x35;
buffer[13] = 0x36;
buffer[14] = 0x2c;
buffer[15] = 0x36;
buffer[16] = 0x31;
buffer[17] = 0x2c;
buffer[18] = 0x39;
buffer[19] = 0x2c;
buffer[20] = 0x34;
buffer[21] = 0x36;
buffer[22] = 0x0d;
buffer[23] = 0x0a;

davekw7x · #2 (**permalink**) March 7th, 2004, 03:52 PM

First of all, your statement that "the string is not ended with \0" is incorrect. In C there is no "string" data type. A string constant, defined by something between pairs of " marks has a number of bytes equal to one more than the number of characters between the " marks.

I assume that BYTE is "#define"d as a char.

Then your statement

Code:

BYTE deliminator[] = "PORT 10,247,56,67,9,46\r\n";

defines a char array that has 25 bytes (the 24 chars between the
" marks and an additional byte that is initialized to '\0'.

How do I know this?

Try the following:

Code:

#include <stdio.h>
#include <string.h>
#define BYTE char


int main()
{
  BYTE mystring[] = "PORT 10,247,56,67,9,46\r\n";
  int i;

  printf("\n\n");

  printf("  sizeof(BYTE) = %d\n", sizeof(BYTE));
  printf("  sizeof(mystring) = %d\n", sizeof(mystring));
  printf("  strlen(mystring) = %d\n", strlen(mystring));

  printf("\n\n");
  for (i = 0; i < sizeof(mystring); i++) {
    printf("<%02X> ", mystring[i]);  }
  printf("\n\n");

  return 0;
}

Now as to your program: Your first call to strtok returns a pointer to the string "10", since it has skipped over the "PORT ". Successive calls return pointers to strings "247", "56", etc.

Note that i is equal to 3 when the pointer to "9" is returned, and i is equal to 4 when the pointer to "46" is returned.

Now you want to convert the strings to integers, so you could use sscanf(), atoi(), or other functions to do so.

The statement

Code:

hi_byte = *str_ptr;

sets hi_byte equal to the ASCII value of the first digit. Not what you want.

I say this, because your function make16() operates on two BYTEs.

By the way, what is an Int8 ? I hope it's not supposed to be an eight-bit integer, since your function must return a 16-bit value.

Dave

Dave