Finally I have a valid reason to learn about memory management. It was also hella weird when encountering it.
Unused memory is wasted memory
this post was submitted on 31 Aug 2025
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Cloud providers LOVE you with this one quick trick!
Also goes for mobile. You use more memory and apps get killed.
and with a good enough leak, the amount of unused memory will become negative!
Not freeing your memory at all is a memory management strategy. I think some LaTeX compilers use it as well as surprisingly many Java applications.
That's the funny thing. I had a (yet) very basic Programm and did not care at all about memory management. When I did some testing I realised, that for some reason when I printed string 1 I also got characters from string 2.
That sounds like it could be memory corruption. That should not happen because every string should be separated by a null terminator.
Sounds interesting, want to share a minimal example?
This is the code I used:
#include <stdio.h>
#include <string.h>
#define MAX_ACCOUNTS 255
typedef struct
{
unsigned int id;
char account_creation_date [10];
char first_name [255];
char last_name [255];
char country_code [2];
unsigned int iban;
char password [255];
double balance;
} account;
account accounts_db[MAX_ACCOUNTS];
unsigned int accounts_created = 0;
account get_account_id (unsigned int id)
{
int i = 0;
while(i < MAX_ACCOUNTS)
{
if(accounts_db[i].id == id)
{
return accounts_db[i];
}
i++;
}
account account;
account.id = -1;
return account;
}
void create_account(char first_name [255], char last_name [255], char password [255], char country_code [2])
{
account new_account;
new_account.id = accounts_created;
strcpy(new_account.first_name, first_name);
strcpy(new_account.last_name, last_name);
strcpy(new_account.password, password);
strcpy(new_account.country_code, country_code);
strcpy(new_account.account_creation_date, "");
new_account.balance = 0.0;
new_account.iban = 0;
accounts_db[accounts_created] = new_account;
accounts_created++;
}
int main()
{
char first_name [255] = "Max";
char last_name [255] = "Mustermann";
char country_code [2] = "DE";
char password [255]= "password";
create_account(first_name, last_name, password,country_code);
account account = get_account_id(0);
printf("Name: %s %s \n", account.first_name, account.last_name);
printf("Account creation date: %s\n", account.account_creation_date);
printf("IBAN: %s %d", account.country_code, account.iban);
}```
When you run it you can see, that behind the country code of the IBAN you get the first two letters of the surenameWithout getting too critical of your code (congrats BTW), never use strcpy instead use strlcpy.
strcpy will happily allow you to create buffer overflows (a common challenge with C) which will cause your application to crash.
You'll find more details here.
Good luck!
Thanks, I did not knew this. I always appreciate constructive criticism. I am quite new to C so theres a shit ton of stuff I have never done or dont even know about.
And understand when you can use them...
I've seen too much code following this advice blindly that just does something like
strncpy(dst, src, strlen(src))
I found the mistake. Since the country code char array only has a size of 2 it overwrites the \0 char causing the memory to leak.
Usually what's meant by a memory leak is memory that's allocated but never freed. Writing outside of array allocation would usually be considered an overflow. Which sounds kinda similar but is not the same.
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.net
Anything I run in C# or similar seems to allocate 512GB of virtual address space and then just populates what it actually uses.
This non-sarcastically. The operating system is better at cleaning up memory than you, and it's completely pointless to free all your allocations if you're about to exit the program. For certain workloads, it can lead to cleaner, less buggy code to not free anything.
It's important to know the difference between a "memory leak" and unfreed memory. A leak refers to memory that cannot be freed because you lost track of the address to it. Leaks are only really a problem if the amount of leaked memory is unbounded or huge. Every scenario is different.
Of course, that's not an excuse to be sloppy with memory management. You should only ever fail to free memory intentionally.
Absolutely. I once wrote a server for a factory machine that spawned child processes to work each job item. Intentionally we did not free any memory in the child process because it serves only one request and then exits anyway. It’s much more efficient to have the OS just clean up everything and provides strong guarantees that nothing can be left behind accidentally for a system where up time was money. Any code to manage memory was pointless line noise and extra developer effort.
In fact I think in the linker we specifically replaced free with a function that does nothing.
Upvoted. This is something I learned rather recently. Sometimes it's more performant to slowly leak than it would be to free properly. Then take x amount of time to restart every n amount of time.
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Back when I was a kid and was learning C, I used to wonder why people considered pointers hard.
My usage of pointers was like:
void func (int * arg1)
{
// do sth with arg1
}
int main ()
{
int x;
func (&x);
return 0;
}
I didn't know stuff like malloc and never felt the need in any of the program logic for the little thingies I made.
Pointers are not hard. Memory management makes it hard.
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You haven't lived until you've produced a memory leak in JavaScript.
Valgrind to the rescue
Congratulations! Now you can get a job at Fortinet.
(Fortinet is a network security vendor...think firewalls, HLBs, etc. They get an ungodly amount of memory leak bugs, or at least far more than you would expect from an enterprise firewall)
Get a job playing Fortnite, got it
(Insert image of Kronk here)
RAII.
Can’t leak what never leaves the stack frame.
Isn’t this for C++?
Classes are just pretentious structs.
is this some genX meme that I'm too millennial to understand?
No. I am just learning C and was curious how long it would take to get my first memory leak.
I think the confusion comes from this not exactly being a positive thing. It reads almost like a new driver saying, "Thank God I finally got my first speeding ticket!"
I did my first "that one thing where you park and want to press breaks but press gas instead by accident."
Gen-x likes to call it "right of passage."
Learn some C you whippersnapper! You ain't gonna become a proper programmer unless you understand your basic low level concepts well!
The youth nowadays, always hiding behind abstractions of abstractions that 90% of the time are just C wrappers anyway /j
(written by an early 20s PHP dev LOL. Although I do plan on learning C quite a bit before I move to C++ and ultimately Rust)
And then OP used valgrind
It'll be fun when you get to funny errors because you used freed memory.
When I was learning about linked lists and decided to use them in a project, I "removed" items by making the previous item's next point to this item's next, except I misplaced a call to free before using the fields, and it somehow still worked most of the time on debug builds, but on optimized builds it would cause a segmentation fault 100% of the time.
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