Problem installing PPCallbacks

I’m having difficulty adding PPCallbacks to the preprocessor. Only the EndOfMainFile() callback is being invoked by Clang. The others are not invoked.

I created a struct that derives from clang::PPCallbacks, and overrides MacroExpands(), MacroDefined(), FileChanged(), and EndOfMainFile() as follows:

struct PPActions : public clang::PPCallbacks {

static int nextSN; // Next serial number

int sn; // this s/n

PPActions() {

sn = nextSN++;

std::cout << “Default PPActions C’tor - instance #” << sn << std::endl;


void MacroExpands(const Token &MacroNameTok, const MacroDefinition &MD,

SourceRange Range, const MacroArgs *Args) override {

using std::cout; using std::endl;

cout << “PPActions::MacroExpands() called!” << endl;


void MacroDefined(const Token &MacroNameTok,

const MacroDirective *MD) override {

using std::cout; using std::endl;

cout << “PPActions::MacroDefined() called” << endl;


void FileChanged(SourceLocation Loc, FileChangeReason Reason,

SrcMgr::CharacteristicKind FileType, FileID PrevFID)

override {

using std::cout; using std::endl;

cout << “PPActions::FileChanged() called” << endl;


// This is the only Callback actually being called.

void EndOfMainFile() override {

using std::cout; using std::endl;

cout << “PPActions::EndOfMainFile() called, instance #” << sn << endl;



I created a class derived from clang:: PreprocessorFrontendAction with the following ExecuteAction() function.

void ExecuteAction() {

using std::cout; using std::endl;

cout << “ToolCppAction::ExecuteAction() called” << endl;

if (compiler->hasPreprocessor()) {

cout << “CompilerInstance has a preprocessor” << endl;

Preprocessor& cpp = compiler->getPreprocessor();

cout << “Installing PPCallbacks…” << endl;

cpp.addPPCallbacks(std::make_unique() );


I’ve also tried installing the callbacks in the BeginSourceFileAction(). The output of that version shows two instances of the callback struct created, and the EndOfMainFile() of both being invoked (but none of the other callbacks).

The problem I’m working involves code analysis on programs using a library whose API consists mostly of macros, so being able to examine macros and their arguments is extremely important.

Any help or insight into this issue would be appreciated.

Best regards,

David Hammer
Principal Developer I
O: 937.433.0477 ext. 140 | M: 937.520.2936


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