Scons自定义依赖扫描器未触发.cpp文件扫描的技术问题

Hey there! Let's break down why your custom scanner only runs on .o object files, and how to adjust it to work with .cpp sources too—adding your extra dependencies alongside SCons' built-in include scanning.

Why It's Only Triggering on .o Files #

SCons comes with a built-in CScanner that automatically handles #include dependencies for C/C++ source files like .cpp. This scanner takes priority over any custom scanners you add globally for .cpp files, which is why your f_scan function never gets called on main.cpp. For .o files, though, there's no dedicated built-in scanner handling their dependencies, so your custom scanner is invoked as expected.

Solution 1: Integrate Custom Scanner with Built-in CScanner #

To make your custom scanner run on .cpp files (alongside the built-in include scanner), you need to add it to the list of scanners that handle C/C++ sources. Update your SConstruct like this:

env = Environment()

def f_scan(node, env, path):
    print("[.] Scanner invoked. -> %s" % str(node))
    return env.File(["dep.txt"])

# Create a scanner targeted at .cpp files
cpp_custom_scanner = Scanner(function=f_scan, skeys=['.cpp'])
# Prepend (or append) your scanner to the built-in C/C++ scanner list
env['CCSCANNER'] = [cpp_custom_scanner] + env['CCSCANNER']

# Keep the .o scanner if you still need it
o_custom_scanner = Scanner(function=f_scan, skeys=['.o'])
env.Append(SCANNERS = o_custom_scanner)

env.Program('main', ['main.cpp'])

Now when SCons processes main.cpp, it will first run your custom scanner to add dep.txt as a dependency, then run the built-in scanner to handle #include references. You'll see your scanner log line for both main.cpp and main.o (if you kept the .o scanner) when you run scons -Q.

Solution 2: Add Fixed Dependencies Directly (Simpler) #

If your only goal is to add a fixed extra dependency like dep.txt to all .cpp files, you don't even need a custom scanner. Use SCons' Depends function instead—it's more straightforward:

env = Environment()

# Target all .cpp files in the project
cpp_files = env.Glob('*.cpp')
# Add dep.txt as a dependency for every .cpp file
env.Depends(cpp_files, 'dep.txt')

env.Program('main', ['main.cpp'])

This will trigger a recompile of all .cpp files whenever dep.txt is modified, exactly like you want.

内容的提问来源于stack exchange，提问作者Vimal Patel