It was weird experiencing the segfault due to strtok(NULL, "\n").

Great! What is strtok_r() function in C language? I compared strtok_r with context against strchr. After testing, I updated the OpenMP demonstration to find the tab character within the string. Now passing: limited length and variable length words, including OpenMP. Update 2 enables parallel sort.

# 15 input files, 1 thread, clang++ -std=c++20
strtok_r  9.655 seconds
strchr    8.713 seconds
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while ( ::fgets(line, MAX_LINE_LEN_L, fh) != NULL ) {
   found = ::strchr(line, '\t');
   count = ::atoll( &line[found - line + 1] );
   line[found - line] = '\0';  // word
   ...
}
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Also, I replaced strlen(...) with found - line.

::memcpy( fixword.data(), line, found - line );
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