fprintf exercise working but the txt is not valid after running - c

Question

I'm having a problem I can't tell what to do. I have this task that asks me to take the words from a file (let's say input.txt) and write them all in another file (let's say output.txt) in the reverse order. The fun part is that when I execute my program (I have a VM of Xubuntu given to me from my University) it's impossible to double click the output.txt file 'cause something's wrong: I'll try to translate it:
"Byte sequence invalid in the conversion's input"
The fun part is that if I do "gedit output.txt" I do see those words all well written how they should be, so I'd say my program "works but corrupts the file". What can be the theoreticals reasons behind this? And if you wanna help me out pointing them, here's a link to my code [EDIT, it seems I can't post the pastebin link. Here's the part that involves the output file]:
`char *t=malloc(sizeof(char)*1025), *tmp;
t=fgets(t,1024,fp);
while(t!=NULL){
tmp=strtok(t, " ");
while(tmp!=NULL){
tmp=strrev(tmp);
fprintf(fo, " %s", tmp);
tmp=strtok(NULL, " ");
}
t=fgets(t,1024,fp);
}`
I hope I didn't break any rule 'cause I'm still new to this site, thanks all!

Answer 1

It's seem there is not a problem with your code itself.
Can you test this and say if your problem is here again ?
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
char *strrev(char *str)
{
int i = 0;
int j = strlen(str) - 1;
while (i < j) {
char tmp = str[i];
str[i] = str[j];
str[j] = tmp;
++i;
--j;
}
return (str);
}
#define BUFFER_LEN 1024
int main(int argc, char* argv[])
{
char line[BUFFER_LEN + 1];
FILE *fp = NULL;
FILE *fo = NULL;
if (argc != 3 && argc != 4) {
fprintf(stderr, "Devi usare 2 o 3 argomenti grz\n");
return -1;
}
if (!(fp = fopen(argv[1],"r"))) { //argv1=input.txt
fprintf(stderr, "Devi \n");
return -1;
}
if (!(fo = fopen(argv[2], (argc == 4 && strcmp(argv[3],"a")) ? "a" : "w"))) {
fprintf(stderr, " 3 argomenti grz\n");
return -1;
}
while(fgets(line, BUFFER_LEN, fp)) {
for (char *word = strtok(line, " "); word; word = strtok(NULL, " ")) {
fprintf(fo, "%s ", strrev(word));
}
}
fclose(fp);
fclose(fo);
return 0;
}
Can you compile & run this code and say if "mousepad" is still losing himself ?
int main(int argc, char* argv[])
{
FILE *fo = NULL;
if (argc != 3 && argc != 4) {
fprintf(stderr, "Devi usare 2 o 3 argomenti grz\n");
return -1;
}
if (!(fo = fopen(argv[2], "w"))) {
fprintf(stderr, " 3 argomenti grz\n");
return -1;
}
fprintf(fo, "test");
fclose(fo);
return 0;
}