libclang get primitive value - c++

Question

How can I get the value of a primitive literal using libclang?
For example, if I have a CXCursor of cursor kind CXCursor_IntegerLiteral, how can I extract the literal value.
UPDATE:
I've run into so many problems using libclang. I highly recommend avoiding it entirely and instead use the C++ interface clang provides. The C++ interface is highly useable and very well documented: http://clang.llvm.org/doxygen/annotated.html
The only purpose I see of libclang now is to generate the ASTUnit object for you as with the following code (it's not exactly easy otherwise):
ASTUnit * astUnit;
{
index = clang_createIndex(0, 0);
tu = clang_parseTranslationUnit(
index, 0,
clangArgs, nClangArgs,
0, 0, CXTranslationUnit_None
);
astUnit = static_cast<ASTUnit *>(tu->TUData);
}
Now you might say that libclang is stable and the C++ interface isn't. That hardly matters, as the time you spend figuring out the AST with libclang and creating kludges with it wastes so much of your time anyway. I'd just as soon spend a few hours fixing up code that does not compile after a version upgrade (if even needed).

Answer 1

Instead of reparsing the original, you already have all the information you need inside the translation unit :
if (kind == CXCursor_IntegerLiteral)
{
CXSourceRange range = clang_getCursorExtent(cursor);
CXToken *tokens = 0;
unsigned int nTokens = 0;
clang_tokenize(tu, range, &tokens, &nTokens);
for (unsigned int i = 0; i < nTokens; i++)
{
CXString spelling = clang_getTokenSpelling(tu, tokens[i]);
printf("token = %s\n", clang_getCString(spelling));
clang_disposeString(spelling);
}
clang_disposeTokens(tu, tokens, nTokens);
}
You will see that the first token is the integer itself, the next one is not relevant (eg. it's ; for int i = 42;.

Answer 2

If you have access to a CXCursor, you can make use of the clang_Cursor_Evaluate function, for example:
CXChildVisitResult var_decl_visitor(
CXCursor cursor, CXCursor parent, CXClientData data) {
auto kind = clang_getCursorKind(cursor);
switch (kind) {
case CXCursor_IntegerLiteral: {
auto res = clang_Cursor_Evaluate(cursor);
auto value = clang_EvalResult_getAsInt(res);
clang_EvalResult_dispose(res);
std::cout << "IntegerLiteral " << value << std::endl;
break;
}
default:
break;
}
return CXChildVisit_Recurse;
}
Outputs:
IntegerLiteral 42

Answer 3

I found a way to do this by referring to the original files:
std::string getCursorText (CXCursor cur) {
CXSourceRange range = clang_getCursorExtent(cur);
CXSourceLocation begin = clang_getRangeStart(range);
CXSourceLocation end = clang_getRangeEnd(range);
CXFile cxFile;
unsigned int beginOff;
unsigned int endOff;
clang_getExpansionLocation(begin, &cxFile, 0, 0, &beginOff);
clang_getExpansionLocation(end, 0, 0, 0, &endOff);
ClangString filename = clang_getFileName(cxFile);
unsigned int textSize = endOff - beginOff;
FILE * file = fopen(filename.c_str(), "r");
if (file == 0) {
exit(ExitCode::CANT_OPEN_FILE);
}
fseek(file, beginOff, SEEK_SET);
char buff[4096];
char * pBuff = buff;
if (textSize + 1 > sizeof(buff)) {
pBuff = new char[textSize + 1];
}
pBuff[textSize] = '\0';
fread(pBuff, 1, textSize, file);
std::string res(pBuff);
if (pBuff != buff) {
delete [] pBuff;
}
fclose(file);
return res;
}

Answer 4

You can actually use a combination of libclang and the C++ interface.
The libclang CXCursor type contains a data field which contains references to the underlying AST nodes.
I was able to successfully access the IntegerLiteral value by casting data[1] to the IntegerLiteral type.
I'm implementing this in Nim so I will provide Nim code, but you can likely do the same in C++.
let literal = cast[clang.IntegerLiteral](cursor.data[1])
echo literal.getValue().getLimitedValue()
The IntegerLiteral type is wrapped like so:
type
APIntObj* {.importcpp: "llvm::APInt", header: "llvm/ADT/APInt.h".} = object
# https://github.com/llvm-mirror/llvm/blob/master/include/llvm/ADT/APInt.h
APInt* = ptr APIntObj
IntegerLiteralObj* {.importcpp: "clang::IntegerLiteral", header: "clang/AST/Expr.h".} = object
IntegerLiteral* = ptr IntegerLiteralObj
proc getValue*(i: IntegerLiteral): APIntObj {.importcpp: "#.getValue()".}
# This is implemented by the superclass: https://clang.llvm.org/doxygen/classclang_1_1APIntStorage.html
proc getLimitedValue*(a: APInt | APIntObj): culonglong {.importcpp: "#.getLimitedValue()".}
Hope this helps someone :)