Creating Variable Sized char Array in C

Question

I am trying to take in a char array that is oversized in order to place delimiters in it based on the variable maxSize

For example if the string "This is a message" is passed to the function along with a maxSize of 4 then the output should be "This, is ,a me,ssag,e"

char *placeDelimiter(char message[], int maxSize) {
  int msgSize = strlen(message);
  int delSize = (msgSize/maxSize);
  int remSize = msgSize%maxSize;
  int newSize = msgSize+delSize;
  if (remSize==0) delSize--; //removes delimiter if on end of char array
  char temp[newSize];
  int delPos = 0;
  for (int x=0;x<msgSize;x++) {
    if ((x+1)%maxSize == 0) temp[x] = ',';
    temp[x+delPos] = message[x];
    delPos = (x+1)/maxSize;
  } 
  return (char *)temp;
}

int main()
{
    char msg[] = "This is a message";
    char *p;
    p = placeDelimiter(msg, 4);
    printf("%s", p);
    return 0;
}

My problem is that I am getting the output "This i," from the input "This is a message" (From an online compiler). Can anyone explain to me what I am doing wrong and how to fix it?

Haris · Accepted Answer · 2015-11-06 13:48:35Z

1

char temp[newSize]; is a local variable to the function placeDelimiter(). Accessing it after the function has returned is Undefined behavior.

You should use dynamic memory allocation.

char* temp = malloc(newSize);

answered Nov 6, 2015 at 13:48

Haris

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