[clang] [clang] replaced the usage of `asctime` with `strftime` (PR #99075)

[Yi-Chi Lee via cfe-commits]

https://github.com/yichi170 created https://github.com/llvm/llvm-project/pull/99075

In `clang/lib/Lex/PPMacroExpansion.cpp`, replaced the usage of the obsolete `asctime` function with `strftime` for generating timestamp strings.

This is my first time contributing to an open-source project. If there is anything that I can improve (such as code quality), please let me know!

Fixes: https://github.com/llvm/llvm-project/issues/98724

>From 0fcbd4a46bb05ad9829fcf33a9829fd5f5269c71 Mon Sep 17 00:00:00 2001
From: yichi170 <ilee900620 at gmail.com>
Date: Wed, 17 Jul 2024 02:15:43 +0800
Subject: [PATCH] [clang] replaced the usage of `asctime` with `strftime`

---
 clang/lib/Lex/PPMacroExpansion.cpp | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/clang/lib/Lex/PPMacroExpansion.cpp b/clang/lib/Lex/PPMacroExpansion.cpp
index 3913ff08c2eb5..f7e657be87932 100644
--- a/clang/lib/Lex/PPMacroExpansion.cpp
+++ b/clang/lib/Lex/PPMacroExpansion.cpp
@@ -1722,10 +1722,12 @@ void Preprocessor::ExpandBuiltinMacro(Token &Tok) {
     // MSVC, ICC, GCC, VisualAge C++ extension.  The generated string should be
     // of the form "Ddd Mmm dd hh::mm::ss yyyy", which is returned by asctime.
     const char *Result;
+    char TimeString[std::size("Ddd Mmm dd hh:mm:ss yyyy")];
     if (getPreprocessorOpts().SourceDateEpoch) {
       time_t TT = *getPreprocessorOpts().SourceDateEpoch;
       std::tm *TM = std::gmtime(&TT);
-      Result = asctime(TM);
+      strftime(TimeString, std::size(TimeString), "%c", TM);
+      Result = TimeString;
     } else {
       // Get the file that we are lexing out of.  If we're currently lexing from
       // a macro, dig into the include stack.
@@ -1735,13 +1737,13 @@ void Preprocessor::ExpandBuiltinMacro(Token &Tok) {
       if (CurFile) {
         time_t TT = CurFile->getModificationTime();
         struct tm *TM = localtime(&TT);
-        Result = asctime(TM);
+        strftime(TimeString, std::size(TimeString), "%c", TM);
+        Result = TimeString;
       } else {
-        Result = "??? ??? ?? ??:??:?? ????\n";
+        Result = "??? ??? ?? ??:??:?? ????";
       }
     }
-    // Surround the string with " and strip the trailing newline.
-    OS << '"' << StringRef(Result).drop_back() << '"';
+    OS << '"' << Result << '"';
     Tok.setKind(tok::string_literal);
   } else if (II == Ident__FLT_EVAL_METHOD__) {
     // __FLT_EVAL_METHOD__ is set to the default value.