c - Delay-Load equivalent in unix based systems

Question

What is the delay load equivalent in unix based system.

I have a code foo.cpp, While compiling with gcc I link it to shared objects(totally three .so files are there.). Each of the .so file for different option.

./foo -v needs libversion.so ./foo -update needs libupdate.so

I need the symbol for those libraries should be resolved only at the run time.

./foo -v should not break even if libupdate.so library is not there.

It is working in windows using the delay load option(in properties of dll). What is its equivalent in unix systems.

Will -lazy option does the same in UNIX? If so, where to include this option: in makefile or with linker ld?

Answer 1

See the reference on your system for dlopen(). You can manually open libraries and resolve external symbols at runtime rather than at link time.

Dug out an example:

int main(int argc, char **argv) {                 
    void *handle=NULL;                                 
    double (*myfunc)(double);                     
    char *err=NULL;                                  

    handle = dlopen ("/lib/libm.so.1", RTLD_LAZY);
    if (!handle) {                                
        err=dlerror();
        perror(err);
        exit(1);                                  
    }                                             

    myfunc = dlsym(handle, "sin");                
    if ((err = dlerror()) != NULL)  {           
        perror(err);
        exit(1);                                  
    }                                             

    printf("sin of 1 is:%f
", (*myfunc)(1.));              
    dlclose(handle);            
    return 0;                  
}