Scanf printing weird characters after the input - c

Question

This code takes in input N-file names and generates N-threads, then the main thread writes something and puts it in a buffer for each thread, and each threads writes their buffer content on their own file. Everything works fine but on the file, the input is like this and i don't know why, hope someone can help me, thanks in advance
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#include <unistd.h>
#include <errno.h>
#include <signal.h>
#include <pthread.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/mman.h>
#include <semaphore.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define fflush(stdin) while (getchar() != '\n')
int n_threads;
FILE **source_files;
char **files;
char buffers[128][128];
pthread_mutex_t *ready;
pthread_mutex_t *done;
char buff[256];
void *thread_function(void *);
int main(int argc, char **argv) {
long i, j, ret;
pthread_t tid;
if (argc < 2) {
printf("Error: Usage -> prog | file1 ... fileN\n");
exit(1);
}
n_threads = argc - 1;
files = argv + 1;
for(i = 0; i < n_threads; i++) {
for(j = 0; j < n_threads; j++) {
if(strcmp(files[i], files[j]) == 0 && i != j) {
puts("Strings are equal.\n");
exit(1);
}
}
}
puts("Strings are different");
/*buffers = (char **)malloc(sizeof(char *) * n_threads);
if(buffers == NULL) {
printf("Malloc error.\n");
exit(1);
}*/
source_files = (FILE **)malloc(sizeof(FILE *) * n_threads);
if(source_files == NULL) {
printf("Malloc error.\n");
exit(1);
}
ready = malloc(sizeof(pthread_mutex_t));
done = malloc(sizeof(pthread_mutex_t));
if (ready == NULL || done == NULL) {
printf("Malloc error.\n");
exit(1);
}
if(pthread_mutex_init(ready, NULL) || pthread_mutex_init(done, NULL) || pthread_mutex_lock(ready)) {
printf("Mutex init error.\n");
exit(1);
}
for(i = 0; i < n_threads; i++) {
if(pthread_create(&tid, NULL, thread_function, (void *) i)) {
printf("Error while creating thread %ld.\n", i);
exit(1);
}
}
//signal(SIG_INT, printer);
i = 0;
while(1) {
if(pthread_mutex_lock(done)) {
printf("Mutex lock error.\n");
exit(1);
}
ret = scanf(" %s", buff);
if(ret == EOF) {
printf("Scanf error.\n");
exit(1);
}
if (ret == 0) {
printf("Non compliant input.\n");
exit(1);
}
getchar();
puts("before strcpy\n");
strcpy(buffers[i],buff);
puts("after strcpy\n");
if(pthread_mutex_unlock(ready)) {
printf("Mutex unlock error.\n");
exit(1);
}
i=(i+1)%n_threads;
}
}
void *thread_function (void *arg) {
int fd;
//FILE *file;
long me = (long) arg;
printf("Thread %ld started.\n", me);
puts("before opening file.\n");
fd = open(files[me], O_CREAT | O_RDWR | O_TRUNC, 0666);
//file = fdopen(fd, "w+");
puts("after opening file.\n");
while(1) {
if(pthread_mutex_lock(ready)) {
printf("Mutex lock error.\n");
exit(1);
}
printf("Thread %ld took string %s.\n", me, buffers[me]);
puts("before fprintf.\n");
//fprintf(file, "%s", buffers[me]);
write(fd, buffers[me], 128);
puts("after fprintf.\n");
if(pthread_mutex_unlock(done)) {
printf("Mutex unlock error.\n");
exit(1);
}
}
}