Split a text file in C and give it a name -

i created code split text files when finds word "new day" , save file specific name.

first, used file_part1, file_part2 , on... however, want use first 15 characters of second line of file reading name of file saved.

for example, second line written: tam 2000-03-07t14:53... want use tam 2000-03-07

the problem function sprintf worked "%d", "%c" not working "%s" , don't have idea why.

i tried print variable before see sprintf should receiving , receiving want...

here code:

int tam_buffer = 75;  int filecounter=1, linecounter=1;  char fileoutputname[16];  int main(int argc, char *argv[]){  char buffer[tam_buffer]; char buffer2[15];   file *arquivo = fopen("entrada.txt", "r"); file *saida;  sprintf(fileoutputname, "file_part%d.txt", filecounter); saida = fopen(fileoutputname, "w");  if(arquivo != null){      while(fgets(buffer, tam_buffer, arquivo)){          if(linecounter==2){         strncpy(buffer2,buffer,14);     }      if (strncmp(buffer,"newday",strlen("newday")) == 0){         fclose(saida);         linecounter = 1;         filecounter++;         printf("%s", buffer2);         sprintf(fileoutputname,"%s", buffer2);         saida = fopen(fileoutputname, "w");         if (!saida)             return 1;            }      fprintf(saida,"%s\n", buffer);     linecounter++;      }  }   fclose(saida); return 0;  } 

if source longer number of characters copy, strncpy function not add string terminator, buffer2 might not contain string terminator , when treat terminated string have undefined behavior.

the solution simple: add terminator manually.

like

strncpy(buffer2,buffer,sizeof buffer2 - 1); buffer2[sizeof buffer2 - 1] = '\0';