dlclose

Learn to close libraries with dlclose.

What is dlclose?

dlclose closes a handle obtained with dlopen. It decrements the reference count; when it reaches zero, the library is unloaded. The int r = dlclose(h); call returns 0 on success and -1 on error.

Closing prevents resource leaks. If a library has been loaded multiple times with dlopen, you need a dlclose for each call. Continuing to work with a closed handle is unsafe; finish your work first, then close. For testing, printf("closed\n") is enough.

The load-close pattern

The simplest flow: void *h = dlopen(NULL, RTLD_LAZY);, if (h) dlclose(h);, printf("closed\n");. Before calling close, make sure symbol work is finished.

For testing, immediately closing the handle and then printf is enough. The output is deterministic. In real apps, you can check the dlclose return and use dlerror on error. If you use multiple libraries, you must call dlclose for each.

Exercise Close the library

Get a handle with void *h = dlopen(NULL, RTLD_LAZY);. Close with if (h) dlclose(h);. Print with printf("closed\n");.

Show example solution

#include <stdio.h>
#include <dlfcn.h>

int main(void) {
    void *h = dlopen(NULL, RTLD_LAZY);
    if (h) dlclose(h);
    printf("closed\n");
    return 0;
}

Test yourself

dlclose call
```
dlclose(____);
```
Show answer
```
dlclose(h);
```
Match dlclose parts

dlclose

Closes handle
0

Success
-1

Error
reference count

Counter
What does dlclose return on success?
- void
- file descriptor
- 0 or -1
- void *
Show answer

0 or -1 — dlclose returns 0 on success, -1 on error.

Next lesson: dlerror

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