FPC RTL coverage

This page lists the 150 Free Pascal library routines and classes that FPC's own code uses most, and says for each whether PXX has it. It was measured on 2026-09-28 with pin v447 (commit 60c5ec9dc0, compiler sha256 fad87004e4e8…), on x86-64 Linux, against fpc 3.2.2.

Of the 150:

The "after v448" column counts five rows as closed by commit 6b34caaf23, which v449 carries: Copy(s, index), Pos(sub, s, offset), UpCase(string), Space and Power. Those five were re-measured on 2026-09-28 with the probe below: with pin v448 (compiler sha256 b2b325036c3b) each still failed as its row says, and with the compiler built at a2614fcb8b (sha256 5dea028059af) each printed what fpc 3.2.2 printed. The other 145 rows were not re-measured.

"Present" means one call gave the same output. It does not mean every overload, option or edge case behaves the same.

How the list was made

The candidates are every routine and class declared in the interface of FPC 3.2.2's System, SysUtils, Classes, StrUtils and Math units, plus the compiler intrinsics such as WriteLn, Inc and SizeOf. That is 938 names. Each name was counted as a whole word, ignoring case, in the 4,894 Pascal sources under /usr/share/fpcsrc/3.2.2/packages (FPC's own packages; Lazarus was not installed). The list is ranked by how many files use the name, and the top 150 are kept. Three internal names (get_frame, StackTop, SPtr) were left out.

A count is a count of words, not of calls. Common words such as Read, Write, Error, Time, Date, Point and Sec are also method, field or variable names, so their counts are too high. The ranking is good enough to choose the 150, but it is not an exact popularity order.

Each name got one probe program:

program probe;
{$mode objfpc}{$H+}
uses SysUtils, Classes, StrUtils, Math;
var s: string;
begin
  s := 'abcdef'; Delete(s, 2, 3); writeln(s);
end.

Each probe was built with fpc -O2 and with the pinned PXX. Both programs were run, and their standard output and exit codes were compared. A probe that FPC refused was fixed until FPC accepted it. When a probe failed in PXX, it was split into smaller probes, one call each, to find the form that fails.

Missing, ranked by use

"Files" is the number of FPC package source files that use the name.

The earlier 28-routine check found three more that are outside this top 150: FormatFloat (20 files), and TStringList.LoadFromFile and SaveToFile. They are covered in Coming from Free Pascal.

Present, but different

A compiler gap found along the way

Passing one character of a string to a var parameter crashes when that string still shares a literal. The same code in FPC prints ayc:

program varchar;
{$mode objfpc}{$H+}
procedure SetC(var c: char); begin c := 'y'; end;
var s: string;
begin
  s := 'abc';
  SetC(s[2]);        { PXX v447: segmentation fault }
  writeln(s);
end.

Assigning s[2] := 'y' directly works, and so does calling UniqueString(s) first. Move(src[1], dst[2], 3) into such a string crashes the same way.

Fixed after v448 (cbbb1e6418, in v449). Measured on 2026-09-28 on x86-64: with pin v448 both programs still stop with a segmentation fault (exit 139); with the compiler built at a2614fcb8b they print ayc and axyze, as FPC does.

All 150