如何在POSIX兼容系统中用C++动态检查库信息及查询版本？

Hey there! Since you're diving into OS concepts and hands-on Linux practice, let's break down your library version questions step by step.

1. Checking GLFW/GLEW Versions on Linux (With Missing Library Checks) #

First, let's cover command-line ways to verify if these libraries are installed and grab their versions:

For GLFW #

• Using pkg-config (most reliable for system-installed libraries):
  Run this command:

  pkg-config --modversion glfw3
  

  If GLFW isn't installed, you'll get a clear error like:

  Package glfw3 was not found in the pkg-config search path.
  Perhaps you should add the directory containing `glfw3.pc'
  to the PKG_CONFIG_PATH environment variable

• For manually compiled/source-installed GLFW:
  Locate the library file (usually in /usr/local/lib or your custom build path) and check its embedded version string:

  strings /usr/local/lib/libglfw.so | grep GLFW_VERSION
  

For GLEW #

• Using pkg-config:

  pkg-config --modversion glew
  

  A missing library will trigger a similar error to GLFW's, indicating the glew.pc config file can't be found.

• Checking the library file directly:

  strings /usr/lib/x86_64-linux-gnu/libGLEW.so | grep GLEW_VERSION
  

  Adjust the path if your library lives in a non-standard location.

2. Dynamic Library Info Checks in C++ (POSIX Systems) #

To programmatically check library versions at runtime on POSIX systems (Linux, BSD, macOS), you'll use the dynamic linking API (dlopen, dlsym, dlclose) from <dlfcn.h>. This lets you load libraries on the fly and query their version info without linking against them at compile time.

Example: Checking GLFW Version Programmatically #

Here's a complete snippet that loads GLFW dynamically and fetches its version string:

#include <iostream>
#include <dlfcn.h>
#include <cstdlib>

int main() {
    // Load the GLFW library (use "libglfw.dylib" instead for macOS)
    void* glfw_handle = dlopen("libglfw.so.3", RTLD_LAZY);
    if (!glfw_handle) {
        std::cerr << "GLFW not installed: " << dlerror() << std::endl;
        return EXIT_FAILURE;
    }

    // Retrieve the address of GLFW's version string function
    const char* (*get_glfw_version)() = 
        reinterpret_cast<const char* (*)()>(dlsym(glfw_handle, "glfwGetVersionString"));
    
    char* error = dlerror();
    if (error) {
        std::cerr << "Failed to access GLFW version function: " << error << std::endl;
        dlclose(glfw_handle);
        return EXIT_FAILURE;
    }

    // Print the detected version
    std::cout << "GLFW Version: " << get_glfw_version() << std::endl;

    // Clean up the loaded library
    dlclose(glfw_handle);
    return EXIT_SUCCESS;
}

Compile this with the dynamic linking flag:

g++ check_glfw_version.cpp -o check_glfw_version -ldl

How This Works #

• dlopen loads the library into your process's memory. RTLD_LAZY delays resolving function addresses until they're actually called, which is more efficient.
• dlsym looks up the address of a specific exposed function (in this case, glfwGetVersionString, which GLFW provides explicitly for version checks).
• Always use dlerror() after dlopen and dlsym to catch missing libraries or undefined symbols.

3. General Methods to Check Installed Library Versions #

For any library on POSIX systems, these are the go-to approaches:

• pkg-config: Works for libraries that provide a .pc configuration file (most open-source libraries). Use:

  pkg-config --modversion <library-name>
  

• System Package Manager: If you installed the library via your distro's package manager:
  • Debian/Ubuntu: dpkg -l | grep <library>
  • Fedora/RHEL: dnf list installed | grep <library>
  • Arch Linux: pacman -Qs <library>
    Note: This only detects packages installed via the manager, not manually compiled ones.
• Library File String Check: Most libraries embed version info in their binary files. Use strings to extract it:

  strings /path/to/library.so | grep -i version
  

• Dynamic Loading in Code: The C++ method shown above works for any library that exposes a version function or symbol. Just check the library's documentation to find the right symbol to query.

内容的提问来源于stack exchange，提问作者Makogan