How to reassign a string? - c

Question

I am trying to write a program which merges a lines from stdin and print only those sentences which are longer than 80 characters. The first found line works well - the later ones, however, are empty. I think that I am doing something wrong with the line
current_sentence = malloc(sentence_len);.
How can I reassign a string correctly?
Code
# include <stdio.h>
# include <stdlib.h>
# include <string.h>
# define BUFFERSIZE 100
char* merge_string(char *text[], int n){
int i;
char *result = malloc(BUFFERSIZE * n);
for (i=0; i < n; i++){
strcat(result, text[i]);
}
return result;
}
int main(int argc, char *argv[]){
char buffer[BUFFERSIZE];
int i = 0;
char *text[BUFFERSIZE];
while(fgets(buffer, BUFFERSIZE, stdin) != NULL){
text[i] = strdup(buffer);
i++;
}
char *sentence = merge_string(text, i);
int sentence_len = strlen(sentence);
int j = 0;
int counter = 0;
char *current_sentence = malloc(sentence_len);
while (j < sentence_len){
current_sentence[counter] = sentence[j];
if (sentence[j] == '\n' && counter >= 80){
printf(":::HIT:::%s\n\n\n", current_sentence);
counter = 0;
current_sentence = malloc(sentence_len);
}
else if (sentence[j] == '\n'){
puts("Resetting counter");
counter = 0;
}
j++; counter++;
}
return 0;
}
Output
make 1_17; ./1_17 < example.txt
make: `1_17' is up to date.
Resetting counter
Resetting counter
:::HIT:::SHenri Cartier-Bresson (1908-2004) said "Your first 10,000 photographs are your worst," but he shot more than one an hour.)
Resetting counter
:::HIT:::
Resetting counter
:::HIT:::

Answer 1

You are not terminating current_sentence with a null character ('\0'). If you want printf to print the string properly, better make sure it is null-terminated.
By the way, there's no need for a second malloc. Reuse the memory allocated for current_sentence without re-allocating.
Also note that you're not freeing the allocated memory properly. You should be use a matching free call for each malloc. Perhaps this isn't a problem now, but it creates a memory leak.
Your loop should look something like this:
while (j < sentence_len)
{
current_sentence[counter] = sentence[j];
if (sentence[j] == '\n')
{
if (counter >= 80)
{
current_sentence[counter + 1] = '\0'; // Make string null-terminated
printf(":::HIT:::%s\n\n\n", current_sentence);
}
else
{
puts("Resetting counter");
}
counter = 0;
}
else
{
counter++;
}
j++;
}
free(current_sentence); // Free allocated memory
Then again, as mentioned in a comment, you'd rather let fgets do the work for you indeed.

Answer 2

char *text[BUFFERSIZE];
should be
char text[BUFFERSIZE];