dlclose
- C course
- Advanced
- Lesson 51/83
- 5 min
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.
Practice Close the library
Get a handle with void *h = dlopen(NULL, RTLD_LAZY);. Close with if (h) dlclose(h);. Print with printf("closed\n");.
Starter code
#include <stdio.h>
#include <dlfcn.h>
// Load library
// Close
// Print
int main(void) {
return 0;
}Sample 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;
}Expected output
closed
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 dlclose call
dlclose(____);dlclose(h);Explanation: dlclose closes the h handle.
2 Match dlclose parts
| Term | Meaning |
|---|---|
dlclose |
Closes handle |
0 |
Success |
-1 |
Error |
reference count |
Counter |
3 What does dlclose return on success?
- void
- file descriptor
- 0 or -1 Correct answer
- void *
Explanation: dlclose returns 0 on success, -1 on error.