building a string

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July 15th, 2002, 03:29 AM

dries

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building a string

i have a function which returns bytes of data 1 at a time.

i want to concatenate that bytes together to get a string

like the gets function does, only i don't get this input from the keyboard

it sounds easy, but i am new to the c language, so i would like to know how to do this

thank you

andre

July 15th, 2002, 11:56 AM

M.Hirsch

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i don´t think there is a pre-made function. you probably need to invent one like this:

void addToString(char *s, char c) {
int len;
len=strlen(s);
(s+len)^=c;
(s+len+1)^=0;
}

this one requires that you allocated enough memory for s before.

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July 15th, 2002, 01:39 PM

Scorpions4ever

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M. Hirsch, the code you posted is conceptually correct, but it looks like you are confusing pascal and c pointer syntax there

. Seriously though, there is a function called strcat, which concatenates two strings (rather than a string and a byte). Maybe you can do something like this:

Code:

void addToString(char *s, char c) {
  char tmp[2];
  tmp[0] = c; tmp[1] = '\0';
  strcat(s, tmp);
}

However, the big issue with the above (the same is true for M. Hirsch's code as well) is that the length of the string is evaluated each time and an extra char is then tacked on to the end. For a long string, this might be a wasteful operation to determine the string length each time. A better way to do this IMHO would be something like this:

Code:

char *ptr;
char ch;
ptr = char_str; // char_str is assumed to be the string array that was allocated previously

while (GetByte(&ch)) {
    *ptr = ch;
    ptr++;
}

*ptr = '\0';

where GetByte() is assumed to be your function that returns a byte at a time. The above code does not recompute the string length each time and is therefore faster.

July 15th, 2002, 05:25 PM