Output Format

Log Output Format

logme produces log messages using a well-defined field order. Individual fields can be enabled, disabled, or formatted using OutputFlags.

The logical order of fields in a log message is:

<time><signature><[proc:thread]><{channel_name}><#subsystem><location><error prefix><code_method><message><eol>

Not all fields are always present. Their presence depends on OutputFlags.

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Field Description

Time

Timestamp of the log message.

Controlled by OutputFlags.Timestamp using TimeFormat:

enum TimeFormat
{
  TIME_FORMAT_NONE,
  TIME_FORMAT_LOCAL,
  TIME_FORMAT_TZ,
  TIME_FORMAT_UTC,
};

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Signature

Single-character severity signature:

• D — Debug
• (empty) — Info
• W — Warning
• E — Error
• C — Critical Error

Info messages intentionally have no signature to reduce visual noise.

Controlled by OutputFlags.Signature.

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[proc:thread]

Process and thread identifier.

• Printed only if ThreadID or ProcessID is enabled
• Format: [proc:thread]
• Either part may be omitted

Thread Naming and Transitions

Threads may be assigned names. If a thread name is set using SetThreadName, the first log entry shows a transition:

:380 -> StartIO

When a name is removed:

:StartIO -> 380

This behavior is controlled by OutputFlags.ThreadTransition.

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{channel_name}

Name of the channel specified by the user when emitting the log message.

This may differ from the channel that actually outputs the message, due to linked channels and routing.

Controlled by OutputFlags.Channel.

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#subsystem

Name of the subsystem associated with the log message.

Subsystems allow logical grouping of messages independently of channels. They can be enabled or disabled selectively.

Controlled by OutputFlags.Subsystem.

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Location

Source code location where the message was emitted.

Controlled by OutputFlags.Location using Detality:

enum Detality
{
  DETALITY_NONE,
  DETALITY_SHORT,
  DETALITY_FULL
};

• NONE — not printed
• SHORT — module name and line
• FULL — full path and line

Printed as:

file:line

---

Error Prefix

Automatically prepended for error-level messages:

• Error:
• Critical:

Controlled by OutputFlags.ErrorPrefix.

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Code Method

Name of the method that emitted the log message.

Printed as:

MethodName():

Controlled by OutputFlags.Method.

Method name shortening

When OutputFlags.Method is enabled, the method name inserted into the log line may become very long (for example, due to namespaces and template parameters). If the same long prefix is repeated on every line, it can significantly bloat log size and reduce readability.

To address this, a channel can be configured with a shortener table. During formatting, the method name text is scanned and configured replacements are applied (long text → short alias). This operation is designed to be very fast and does not perform memory allocations in the replacement hot path.

Example:

static const Logme::ShortenerPair shorteners[] =
{
  {"nghttp2::DirectReader", "[dreader]"},
  {"Syncme::Socket", "[skt]"},
  {nullptr, nullptr}
};

pch->SetShortenerPair(shorteners);

Result:

2026-02-12 21:12:08:950   [:Autodetect] [skt]::SetOptions(): server: TCP_NODELAY was set to true
2026-02-12 21:13:17:278   [:RSVal] [dreader]::Read(): 1: sent 1554 (remains 0)

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Message

The actual user-provided log message.

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EOL

End-of-line character.

Controlled by OutputFlags.Eol.