C: fprintf does not work - c

Question

I have a long C code. At the beginning I open two files and write something on them:
ffitness_data = fopen("fitness_data.txt","w");
if( ffitness_data == NULL){
printf("Impossible to open the fitness data file\n");
exit(1);
}else{
fprintf(ffitness_data,"#This file contains all the data that are function of fitness.\n");
fprintf(ffitness_data,"#Columns: f,<p>(f),<l>(f).\n\n");
}
fmeme_data = fopen("meme_data.txt","w");
if( fmeme_data == NULL){
printf("Impossible to open the meme data file\n");
exit(1);
}else{
fprintf(fmeme_data,"#This file contains all the data relative to memes.\n");
fprintf(fmeme_data,"#Columns: fitness, popularity, lifetime.\n\n");
}
Everything is fine at this step: files are open and two lines are written on them.
Then I have a long simluation of a stochastic process, whose code is not interesting for the question's purposes: the files and their pointers are never used. At the end of the process I have:
for(i=0;i<data;i++){
fprintf(fmeme_data,"%f\t%d\t%f\n",meme[i].fitness,meme[i].popularity,meme[i].lifetime);
}
for(i=0;i<40;i++){
fprintf(ffitness_data,"%f\t%f\t%f\n",(1.0/40)*(i+0.5),popularity_histo[i],lifetime_histo[i]);
}
Then I DO fflush() and fclose() of both files.
If I make the code run on my laptop, both files are filled. If the code runs on a remote server, the file fitness_data.txt contains only the first print, i.e. the print starting with # but doesn't contain the data. I want you to note that:
The other file never gives me problems.
I'm used to this server. Something similar never happened.
Given all these information, the question is:
Why it is happening that a certain command, used always in the same way and in the same code, always works on a server while on a different server it works sometime but sometime it doesn't?
Admins: I don't think this question is a duplicate. All similar questions were solved by asjusting the code (here) or adding fflush() (here) and similar things. Here is not a problem in the code (in my modest opinion) because on my laptop it works. I bet it works on most.

Answer 1

We can't say for certain what's going on here, because we don't have your full program nor do we have access to the server where the problem happens. But, we can give you some debugging advice.
When a C program behaves differently on one computer than another, the very first thing you should suspect is memory corruption. The best available tool for finding memory corruption is valgrind. Fix the first invalid operation it reports and repeat until it reports no more invalid operations. There are excellent odds that the problem will have then gone away.
Turn up the warning levels as high as they can go and fix all of the complaints, even the ones that look silly.
You say you are calling fflush and fclose, but are you checking whether they failed? Check thoroughly, like this:
if (ferror(ffitness_data) || fflush(ffitness_data) || fclose(ffitness_data)) {
perror("write error on fitness_data.txt");
exit(1);
}
Does the problem go away if you change the optimization level you are compiling with? If so, you may have a bug that causes "undefined behavior". Unfortunately there are a lot of possible ways to do that and I can't easily explain how to look for them.
Use a tool like C-Reduce to cut your program down to a smaller program that still doesn't work correctly but is short enough to post here in its entirety.
Read and follow the instructions in the article "How to Debug Small Programs"..