Converting a C string to a Pascal-style string

Question

I am trying to convert a normal C string into a Pascal string. I am running into trouble when I need to assign the first index of the pascal string to be the length of the string. I'll place my code below, but I cannot seem to figure out how to convert the length of the original string (especially when it is over 10), slen, into a char that can then be assigned to an index.

char pascal[slen];
char pascalFirst = slen + '0';  //Having such a hard time assigning pascal[0]
printf("%c\n", pascalFirst);
pascal[0] = pascalFirst;

printf("%s pasFirst\n", pascal);

for (int i =0 ; i < strlen(pascal); i++){
    pascal[i+1] = s[i];

}
printf("%s\n", pascal);

honestly @tadman I saw somewhere else someone did that so I gave it a try. — vynabhnnqwxleicntw
– vynabhnnqwxleicntw, Commented Sep 14, 2020 at 22:55
'0' is the ASCII value of zero (48) and shouldn't be there. Don't go down the road of Cargo Cult Programming. If you see someone do something that's where you need to stop, think, and understand what they're attempting before just mimicking what they did. The Pascal string format requires the first byte to be the length expressed as an unsigned char, not an ASCII value of any kind. Not trying to bust on you here, but C is an extremely unforgiving language and just pasting in arbitrary code can get you into heaps of trouble. — tadman
– tadman, Commented Sep 14, 2020 at 22:55
He is confusing the fact that the first 'char' of the string is not an ascii value for the length, but is the actual number from 0-255. Easy to do if you don't understand what the first byte actually represents. — Michael Dorgan
– Michael Dorgan, Commented Sep 14, 2020 at 22:57

tadman · Accepted Answer · 2020-09-14 22:54:06Z

1

It should be a simple as:

char* to_pstr(char* src) {
  char* p = malloc(strlen(src) + 1);

  *((unsigned char*) p) = strlen(src);
  strncpy(src, &p[1], strlen(src));

  return p;
}

Where this of course presumes that src is <= 255 characters long.

edited Sep 14, 2020 at 22:54

answered Sep 14, 2020 at 22:52

tadman

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1 Comment

Michael Dorgan Over a year ago

With the reminder that you need to free that string as it has been dynamically allocated.

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