C : Dynamically storing strings (of dynamic sizes!)? -

am missing incredibly simple? because can't seem find reason why code isn't storing strings dynamically. blank lines when print them @ end. supposed print last "n" lines of arbitrary number of lines. there seems problem storage of actual lines though. can lend hand?

this not hw way. problem k&r book (whose answers online). i'm trying learn c on own.

void tail5_13(int n) {      int maxpoint = 3;     size_t *maxlength;     *maxlength = sizeof(char) * 10;      char **pointptr = malloc(sizeof(void *) * maxpoint);     char **pointcnt = pointptr;      char *lineptr = malloc(sizeof(char) * *maxlength);      int numlines = 0;     int printnum = 0;     int c;        while((c = getline(&lineptr, maxlength, stdin)) > 1)     {         if(numlines < maxpoint)         {             storeline5_13(pointcnt, lineptr, c);             pointcnt++;         }         else         {             maxpoint *= 2;             printf("increased pointer amount %d\n", maxpoint);             pointptr = (char **) realloc(pointptr, sizeof(void *) * maxpoint);             storeline5_13(pointcnt, lineptr, c);             pointcnt++;         }         numlines++;     }      if(n <= numlines)         printnum = n;     else         printnum = numlines;      while(printnum-- > 0 )     {         printf("%s\n", *(pointcnt-1));     }  }    void storeline5_13(char** pointcnt, char* line, int length) {       *pointcnt = (char *) malloc(sizeof(char) * length);      while(*line != '\n')     {         *((*pointcnt)++) = *line++;      }      **pointcnt = '\0';   } 

size_t *maxlength; *maxlength = sizeof(char) * 10; 

you're dereferencing wild (unassigned) pointer.

instead, should be:

size_t maxlength = sizeof(char) * 10; // ... char *lineptr = malloc(sizeof(char) * maxlength); // ... while((c = getline(&lineptr, &maxlength, stdin)) > 1) 

then, you're using automatic variable.