Summary - Dynamic loading

Combine dlopen and dlsym to write a plugin system.

Dynamic loading summary

You learned the dynamic loading toolkit: dlopen loads a library, dlsym resolves a symbol, dlclose closes, dlerror catches errors. These are the core of plugin systems, interpreters and modular architecture.

In this summary we will combine the four tools into a dl preparation app. Using them together shows how a real plugin system is built. The output is deterministic: we print a fixed ready message.

Exercise Prepare dl

Clear the old error with dlerror();. Load with void *h = dlopen(NULL, RTLD_LAZY);. Get the symbol with void *sym = NULL; if (h) { sym = dlsym(h, "printf"); }. (void)sym;. Print with printf("dl ready\n");. Close with if (h) dlclose(h);.

Show example solution

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

int main(void) {
    dlerror();
    void *h = dlopen(NULL, RTLD_LAZY);
    void *sym = NULL;
    if (h) {
        sym = dlsym(h, "printf");
    }
    (void)sym;
    printf("dl ready\n");
    if (h) dlclose(h);
    return 0;
}

Next steps

You completed dynamic loading. These foundations are the core of plugin systems, scripting language interpreters and modular service architecture. Load with dlopen, call with dlsym, guard with dlerror.

Next topic: cryptography basics. You will learn data integrity and confidentiality with hash, HMAC, AES and secure random numbers. Combined with dynamic loading, you can for instance load OpenSSL at runtime and use it.

Test yourself

Which function should be called first?
- dlclose
- dlopen
- dlsym
- dlerror
Show answer

dlopen — dlopen is called first; then dlsym, finally dlclose.
Match dl functions

dlopen

Loads
dlsym

Resolves
dlclose

Closes
dlerror

Errors

Next lesson: Hash functions

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