Member Avatar for az_ez

Hi,
I've been working on this code but recently there's been a problem with a section of my code, this being that there was a stack overload but now, the code just stays in a loop saying that there is an invald arguement. I don't know how to get it to finish and open the file to write to it.
Any help would be appreciated!
This is the code:

void writefile()
{
	char writefile[1000000];
	
	char openfile [20];
	
         FILE * pFile;
	
         cout << "\nFile name to open: ";
	cin >> openfile;
	
         pFile = fopen (openfile ,"w");

                   if (pFile == NULL) perror ("Error opening file");
		 else {
	
         cout<<"Enter text:"<<endl;
	cin>>writefile;

	fputs(writefile, pFile);
	fclose (pFile);
}
}
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  • Latest Post Latest Post by az_ez

Dani AI

Generated

A few focused points to finish this thread and make the code robust.

The immediate problem is very likely twofold: large automatic buffers and an attempt to use a stream that failed to open. As pointed out, putting a megabyte array on the stack is unreliable and can cause crashes that look like “infinite loops” or runtime assertions. ’s use of line-based input is the right direction for reading text, but the buffer-size issue and a missing open-check can still produce the assertion that the stream is NULL.

A compact, modern approach is to use std::string and std::ofstream and to check the stream open state before writing. Example pattern:

#include <iostream>
#include <fstream>
#include <string>

void writefile() {
    std::string filename;
    std::getline(std::cin, filename);
    std::ofstream out(filename);
    if (!out.is_open()) { std::cerr << "Failed to open: " << filename << "\n"; return; }
    std::string line;
    while (std::getline(std::cin, line) && line != ".") out << line << '\n';
}

Troubleshooting checklist (quick): print the filename right after reading it to confirm contents; try opening a known-good name like "test.txt"; check current working directory and file permissions; if using C APIs check fopen’s return and call perror(errno) to see the OS error; run under the debugger to see which call triggers the assertion. Also avoid naming a variable the same as the function (keeps code clearer).

Summary: replace large fixed buffers with heap-managed types (std::string or std::vector), read lines with std::getline, always verify the file opened before writing, and use clear error messages (print the filename and errno) to find why the open failed. This addresses the stack/overflow and the stream != NULL assertion that reported.

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All 7 Replies

Member Avatar for caut_baia

So .. where is the problem ?

Member Avatar for az_ez

The problm is that when text is entered, it immediately says that there is an error and goes into an infinite loop which i dont know how to stop it, aswell as not saving the text entered

Member Avatar for gerard4143

You posted code that doesn't contain a loop.

Member Avatar for az_ez

oh well i figured it had something to do with the if statement but I dont know if theres anything wrong with it

Member Avatar for gerard4143

I tried the code below and it worked.

#include <iostream>
#include <cstdio>

using namespace std;

void writefile()
{
	char writefile[1000000];
	
	char openfile [20];
	
         FILE * pFile;
	
         cout << "\nFile name to open: ";
	 cin.getline(openfile, 20);
	
         pFile = fopen (openfile ,"w");

                   if (pFile == NULL) perror ("Error opening file");
		 else {
	
        cout<<"Enter text->";
	cin.getline(writefile, 1000000);

	fputs(writefile, pFile);
	fclose (pFile);
}
}

int main()
{
  writefile();
  return 0;
}
Member Avatar for nezachem

Two problems with the code. An immediate and major one is that

char writefile[1000000];

attempt to allocate one million characters (that is one megabyte) on the stack. The stack is a very limited resource. For example, Windows by default gives one megabyte for the whole stack, and by the time your function is called part of it is already in use. No wonders you have a stack overflow. Never ever allocate large objects in automatic storage.

Problem number two is

void writefile()
{
	char writefile[1000000];

Giving a function and a variable same names may or may not cause a headache to a compiler. It certainly causes one to a reviewer.

> I tried the code below and it worked.

This is probably the most unprofessional way to answer the question.

Edited by nezachem because: n/a
Member Avatar for az_ez

Than you, that was really helpful in explaining what was wrong. When I change the size of the array now and change the name I get an assertion error expression:(stream!=NULL) and so I dont know what to do with that either

but thank you!

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