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std: add fmt option to escape non-printable characters #6218

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Sep 2, 2020
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std: add fmt option to escape non-printable characters #6218

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17 changes: 17 additions & 0 deletions lib/std/fmt.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -66,6 +66,7 @@ fn peekIsAlign(comptime fmt: []const u8) bool {
/// - output numeric value in hexadecimal notation
/// - `s`: print a pointer-to-many as a c-string, use zero-termination
/// - `B` and `Bi`: output a memory size in either metric (1000) or power-of-two (1024) based notation. works for both float and integer values.
/// - `e` and `E`: if printing a string, escape non-printable characters
/// - `e`: output floating point value in scientific notation
/// - `d`: output numeric value in decimal notation
/// - `b`: output integer value in binary notation
Expand Down Expand Up @@ -599,6 +600,16 @@ pub fn formatText(
try formatInt(c, 16, fmt[0] == 'X', FormatOptions{ .width = 2, .fill = '0' }, writer);
}
return;
} else if (comptime (std.mem.eql(u8, fmt, "e") or std.mem.eql(u8, fmt, "E"))) {
for (bytes) |c| {
if (std.ascii.isPrint(c)) {
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Do we consider \t, \n and \r printable? (#4014)

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For purposes of a debug print: I don't think they should be considered printable:

  • its hard to visually tell the difference between a tab that is one space wide an a normal space character.
  • I imagine this would often be used for line based output, where escaping newlines is desired.
  • \r is unprintable

try writer.writeByte(c);
} else {
try writer.writeAll("\\x");
try formatInt(c, 16, fmt[0] == 'E', FormatOptions{ .width = 2, .fill = '0' }, writer);
}
}
return;
} else {
@compileError("Unknown format string: '" ++ fmt ++ "'");
}
Expand Down Expand Up @@ -1319,6 +1330,12 @@ test "slice" {
try testFmt("buf: Test\n Other text", "buf: {s}\n Other text", .{"Test"});
}

test "escape non-printable" {
try testFmt("abc", "{e}", .{"abc"});
try testFmt("ab\\xffc", "{e}", .{"ab\xffc"});
try testFmt("ab\\xFFc", "{E}", .{"ab\xffc"});
}

test "pointer" {
{
const value = @intToPtr(*align(1) i32, 0xdeadbeef);
Expand Down