# Dynamic Linker

The names in `Base.Libdl` are not exported and need to be called e.g. as `Libdl.dlopen()`.

`dlopen`(libfile::AbstractString[, flags::Integer])

  Load a shared library, returning an opaque handle.

  The optional flags argument is a bitwise-or of zero or more of `RTLD_LOCAL`, `RTLD_GLOBAL`, `RTLD_LAZY`, `RTLD_NOW`, `RTLD_NODELETE`, `RTLD_NOLOAD`, `RTLD_DEEPBIND`, and `RTLD_FIRST`. These are converted to the corresponding flags of the POSIX (and/or GNU libc and/or MacOS) dlopen command, if possible, or are ignored if the specified functionality is not available on the current platform. The default flags are platform specific. On MacOS the default `dlopen` flags are `RTLD_LAZY|RTLD_DEEPBIND|RTLD_GLOBAL` while on other platforms the defaults are `RTLD_LAZY|RTLD_DEEPBIND|RTLD_LOCAL`. An important usage of these flags is to specify non default behavior for when the dynamic library loader binds library references to exported symbols and if the bound references are put into process local or global scope. For instance `RTLD_LAZY|RTLD_DEEPBIND|RTLD_GLOBAL` allows the library’s symbols to be available for usage in other shared libraries, addressing situations where there are dependencies between shared libraries.

`dlopen_e`(libfile::AbstractString[, flags::Integer])

  Similar to `dlopen()`, except returns a `NULL` pointer instead of raising errors.

`RTLD_DEEPBIND`
`RTLD_FIRST`
`RTLD_GLOBAL`
`RTLD_LAZY`
`RTLD_LOCAL`
`RTLD_NODELETE`
`RTLD_NOLOAD`
`RTLD_NOW`

  Enum constant for `dlopen()`. See your platform man page for details, if applicable.

`dlsym`(handle, sym)

  Look up a symbol from a shared library handle, return callable function pointer on success.

`dlsym_e`(handle, sym)

  Look up a symbol from a shared library handle, silently return `NULL` pointer on lookup failure.

`dlclose`(handle)

  Close shared library referenced by handle.

`dlext`

  File extension for dynamic libraries (e.g. dll, dylib, so) on the current platform.

`find_library`(names, locations)

  Searches for the first library in `names` in the paths in the `locations` list, `DL_LOAD_PATH`, or system library paths (in that order) which can successfully be dlopen’d. On success, the return value will be one of the names (potentially prefixed by one of the paths in locations). This string can be assigned to a `global const` and used as the library name in future `ccall`‘s. On failure, it returns the empty string.

`DL_LOAD_PATH`

  When calling `dlopen()`, the paths in this list will be searched first, in order, before searching the system locations for a valid library handle.