Undefined symbol std::__1::__hash_memory(void const*, unsigned long)

[ncihnegn]

hash_memory.cc:

#include <unordered_map>
#include <string>

using namespace std;

int main() {
  unordered_map<string, int> m;
  m["test"]=0;
  return 0;
}

$ /usr/local/opt/llvm/bin/clang++ -std=c++26 hash_memory.cc                            
Undefined symbols for architecture arm64:
  "std::__1::__hash_memory(void const*, unsigned long)", referenced from:
      unsigned long std::__1::__do_string_hash[abi:ne210101]<char const*>(char const*, char const*) in hash_memory-8f4180.o
ld: symbol(s) not found for architecture arm64
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
$ /usr/local/opt/llvm/bin/clang++ --version                                             
clang version 21.1.2
Target: arm64-apple-darwin25.0.0
Thread model: posix
InstalledDir: /usr/local/Cellar/llvm/21.1.2/bin

[keinflue]

Same as in #161947:

The program is missing #include<string> and therefore isn't guaranteed to compile or behave as expected.

[ncihnegn]

#include <string> doesn't change the behavior.

[ncihnegn]

Found a workaround in Homebrew/homebrew-core#235411

[keinflue]

In that case this looks like a duplicate of #155531 and #77653.