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Currently in the entire C API of WPILib we have ~8 different ways of handling strings. The C API actually isn't built for pure C callers (We don't actually have any of those). Instead, they're built for interop between languages like LabVIEW and C# which can talk to C API's directly. For output parameters, the choice was fairly obvious. An output struct containing a const string pointer and a length makes the most sense. Its easy to use these from most other languages, and doesn't require special null termination handling. Freeing these is also easy, as if you ever receive one of these string structures, theres just a single function call to free it. Input parameters are a bit more complex. To be used from pure C, and from LabVIEW, a null terminated string is the best in most cases. However, null terminated strings in general have a lot of downsides. Additionally, from LabVIEW there are other considerations around encoding that having a wrapper struct helps make a bit easier. From a language like C#, a wrapper struct is by far the easiest, as custom marshalling can make it trivial to marshal both UTF8 and UTF16 strings down. The final consideration is its nice to have an identical concept for both input and output. It makes the rules fairly easy to understand. WPILib will not have any APIs that manipulate a string allocated externally. This means WPI_String can be const, as across the boundary it is always const. If a WPILib API takes a const WPI_String*, WPILib will not manipulate or attempt to free that string, and that string is treated as an input. It is up to the caller to handle that memory, WPILib will never hold onto that memory longer than the call. If a WPILib API takes a WPI_String*, that string is an output. WPILib will allocate that API with WPI_AllocateString(), fill in the string, and return to the caller. When the caller is done with the string, they must free it with WPI_FreeString(). If an output struct contains a WPI_String member, that member is considered read only, and should not be explicitly freed. The caller should call the free function for that struct. If an array of WPI_Strings are returned, each individual string is considered read only, and should not be explicitly freed. The free function for that array should be called by the caller. If an input struct containing a WPI_String, or an input array of WPI_Strings is passed to WPILib, the individual strings will not be manipulated or freed by WPILib, and the caller owns and should free that memory. Callbacks also follow these rules. The most common is a callback either getting passed a const WPI_String* or a struct containing a WPI_String. In both of these cases, the callback target should consider these strings read only, and not attempt to free them or manipulate them.
313 lines
11 KiB
C
313 lines
11 KiB
C
// Copyright (c) FIRST and other WPILib contributors.
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// Open Source Software; you can modify and/or share it under the terms of
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// the WPILib BSD license file in the root directory of this project.
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#pragma once
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#include <stddef.h> // NOLINT
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#include <stdint.h>
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#include <wpi/string.h>
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#ifdef __cplusplus
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extern "C" {
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#endif
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/** C-compatible data log (opaque struct). */
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struct WPI_DataLog;
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/**
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* Construct a new Data Log.
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*
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* @param filename filename to use
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* @param errorCode error if file failed to open (output)
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* @param extraHeader extra header data
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*/
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struct WPI_DataLog* WPI_DataLog_CreateWriter(
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const struct WPI_String* filename, int* errorCode,
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const struct WPI_String* extraHeader);
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/**
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* Construct a new Data Log background writer. The log will be initially
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* created with a temporary filename.
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*
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* @param dir directory to store the log
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* @param filename filename to use; if none provided, a random filename is
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* generated of the form "wpilog_{}.wpilog"
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* @param period time between automatic flushes to disk, in seconds;
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* this is a time/storage tradeoff
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* @param extraHeader extra header data
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*/
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struct WPI_DataLog* WPI_DataLog_CreateBackgroundWriter(
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const struct WPI_String* dir, const struct WPI_String* filename,
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double period, const struct WPI_String* extraHeader);
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/**
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* Construct a new Data Log background writer that passes its output to the
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* provided function rather than a file. The write function will be called on a
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* separate background thread and may block. The write function is called with
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* an empty data array (data=NULL, len=0) when the thread is terminating.
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*
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* @param write write function
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* @param ptr pointer to pass to write function ptr parameter
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* @param period time between automatic calls to write, in seconds;
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* this is a time/storage tradeoff
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* @param extraHeader extra header data
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*/
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struct WPI_DataLog* WPI_DataLog_CreateBackgroundWriter_Func(
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void (*write)(void* ptr, const uint8_t* data, size_t len), void* ptr,
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double period, const struct WPI_String* extraHeader);
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/**
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* Change log filename. Can only be used on background writer data logs.
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*
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* @param datalog data log
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* @param filename filename
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*/
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void WPI_DataLog_SetBackgroundWriterFilename(struct WPI_DataLog* datalog,
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const struct WPI_String* filename);
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/**
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* Releases a data log object. Closes the file and returns resources to the
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* system.
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*
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* @param datalog data log
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*/
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void WPI_DataLog_Release(struct WPI_DataLog* datalog);
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/**
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* Explicitly flushes the log data to disk.
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*
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* @param datalog data log
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*/
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void WPI_DataLog_Flush(struct WPI_DataLog* datalog);
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/**
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* Pauses appending of data records to the log. While paused, no data records
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* are saved (e.g. AppendX is a no-op). Has no effect on entry starts /
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* finishes / metadata changes.
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*
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* @param datalog data log
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*/
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void WPI_DataLog_Pause(struct WPI_DataLog* datalog);
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/**
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* Resumes appending of data records to the log. If called after Stop(),
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* opens a new file (with random name if SetFilename was not called after
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* Stop()) and appends Start records and schema data values for all previously
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* started entries and schemas.
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*
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* @param datalog data log
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*/
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void WPI_DataLog_Resume(struct WPI_DataLog* datalog);
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/**
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* Stops appending all records to the log, and closes the log file.
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*
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* @param datalog data log
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*/
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void WPI_DataLog_Stop(struct WPI_DataLog* datalog);
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/**
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* Start an entry. Duplicate names are allowed (with the same type), and
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* result in the same index being returned (Start/Finish are reference
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* counted). A duplicate name with a different type will result in an error
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* message being printed to the console and 0 being returned (which will be
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* ignored by the Append functions).
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*
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* @param datalog data log
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* @param name Name
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* @param type Data type
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* @param metadata Initial metadata (e.g. data properties)
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* @param timestamp Time stamp (may be 0 to indicate now)
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*
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* @return Entry index
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*/
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int WPI_DataLog_Start(struct WPI_DataLog* datalog,
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const struct WPI_String* name,
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const struct WPI_String* type,
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const struct WPI_String* metadata, int64_t timestamp);
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/**
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* Finish an entry.
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*
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* @param datalog data log
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* @param entry Entry index
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* @param timestamp Time stamp (may be 0 to indicate now)
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*/
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void WPI_DataLog_Finish(struct WPI_DataLog* datalog, int entry,
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int64_t timestamp);
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/**
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* Updates the metadata for an entry.
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*
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* @param datalog data log
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* @param entry Entry index
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* @param metadata New metadata for the entry
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* @param timestamp Time stamp (may be 0 to indicate now)
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*/
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void WPI_DataLog_SetMetadata(struct WPI_DataLog* datalog, int entry,
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const struct WPI_String* metadata,
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int64_t timestamp);
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/**
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* Appends a raw record to the log.
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*
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* @param datalog data log
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* @param entry Entry index, as returned by WPI_DataLog_Start()
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* @param data Byte array to record
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* @param len Length of byte array
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* @param timestamp Time stamp (may be 0 to indicate now)
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*/
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void WPI_DataLog_AppendRaw(struct WPI_DataLog* datalog, int entry,
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const uint8_t* data, size_t len, int64_t timestamp);
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/**
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* Appends a boolean record to the log.
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*
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* @param datalog data log
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* @param entry Entry index, as returned by WPI_DataLog_Start()
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* @param value Boolean value to record
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* @param timestamp Time stamp (may be 0 to indicate now)
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*/
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void WPI_DataLog_AppendBoolean(struct WPI_DataLog* datalog, int entry,
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int value, int64_t timestamp);
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/**
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* Appends an integer record to the log.
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*
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* @param datalog data log
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* @param entry Entry index, as returned by WPI_DataLog_Start()
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* @param value Integer value to record
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* @param timestamp Time stamp (may be 0 to indicate now)
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*/
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void WPI_DataLog_AppendInteger(struct WPI_DataLog* datalog, int entry,
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int64_t value, int64_t timestamp);
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/**
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* Appends a float record to the log.
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*
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* @param datalog data log
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* @param entry Entry index, as returned by WPI_DataLog_Start()
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* @param value Float value to record
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* @param timestamp Time stamp (may be 0 to indicate now)
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*/
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void WPI_DataLog_AppendFloat(struct WPI_DataLog* datalog, int entry,
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float value, int64_t timestamp);
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/**
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* Appends a double record to the log.
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*
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* @param datalog data log
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* @param entry Entry index, as returned by WPI_DataLog_Start()
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* @param value Double value to record
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* @param timestamp Time stamp (may be 0 to indicate now)
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*/
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void WPI_DataLog_AppendDouble(struct WPI_DataLog* datalog, int entry,
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double value, int64_t timestamp);
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/**
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* Appends a string record to the log.
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*
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* @param datalog data log
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* @param entry Entry index, as returned by WPI_DataLog_Start()
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* @param value String value to record
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* @param timestamp Time stamp (may be 0 to indicate now)
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*/
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void WPI_DataLog_AppendString(struct WPI_DataLog* datalog, int entry,
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const struct WPI_String* value,
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int64_t timestamp);
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/**
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* Appends a boolean array record to the log.
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*
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* @param datalog data log
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* @param entry Entry index, as returned by WPI_DataLog_Start()
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* @param arr Boolean array to record
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* @param len Number of elements in array
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* @param timestamp Time stamp (may be 0 to indicate now)
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*/
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void WPI_DataLog_AppendBooleanArray(struct WPI_DataLog* datalog, int entry,
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const int* arr, size_t len,
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int64_t timestamp);
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/**
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* Appends a boolean array record to the log.
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*
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* @param datalog data log
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* @param entry Entry index, as returned by WPI_DataLog_Start()
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* @param arr Boolean array to record
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* @param len Number of elements in array
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* @param timestamp Time stamp (may be 0 to indicate now)
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*/
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void WPI_DataLog_AppendBooleanArrayByte(struct WPI_DataLog* datalog, int entry,
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const uint8_t* arr, size_t len,
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int64_t timestamp);
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/**
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* Appends an integer array record to the log.
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*
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* @param datalog data log
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* @param entry Entry index, as returned by WPI_DataLog_Start()
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* @param arr Integer array to record
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* @param len Number of elements in array
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* @param timestamp Time stamp (may be 0 to indicate now)
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*/
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void WPI_DataLog_AppendIntegerArray(struct WPI_DataLog* datalog, int entry,
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const int64_t* arr, size_t len,
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int64_t timestamp);
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/**
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* Appends a float array record to the log.
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*
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* @param datalog data log
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* @param entry Entry index, as returned by WPI_DataLog_Start()
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* @param arr Float array to record
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* @param len Number of elements in array
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* @param timestamp Time stamp (may be 0 to indicate now)
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*/
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void WPI_DataLog_AppendFloatArray(struct WPI_DataLog* datalog, int entry,
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const float* arr, size_t len,
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int64_t timestamp);
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/**
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* Appends a double array record to the log.
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*
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* @param datalog data log
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* @param entry Entry index, as returned by WPI_DataLog_Start()
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* @param arr Double array to record
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* @param len Number of elements in array
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* @param timestamp Time stamp (may be 0 to indicate now)
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*/
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void WPI_DataLog_AppendDoubleArray(struct WPI_DataLog* datalog, int entry,
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const double* arr, size_t len,
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int64_t timestamp);
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/**
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* Appends a string array record to the log.
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*
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* @param datalog data log
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* @param entry Entry index, as returned by WPI_DataLog_Start()
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* @param arr String array to record
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* @param len Number of elements in array
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* @param timestamp Time stamp (may be 0 to indicate now)
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*/
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void WPI_DataLog_AppendStringArray(struct WPI_DataLog* datalog, int entry,
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const struct WPI_String* arr, size_t len,
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int64_t timestamp);
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void WPI_DataLog_AddSchemaString(struct WPI_DataLog* datalog,
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const struct WPI_String* name,
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const struct WPI_String* type,
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const struct WPI_String* schema,
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int64_t timestamp);
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void WPI_DataLog_AddSchema(struct WPI_DataLog* datalog,
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const struct WPI_String* name,
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const struct WPI_String* type, const uint8_t* schema,
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size_t schema_len, int64_t timestamp);
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#ifdef __cplusplus
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} // extern "C"
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#endif
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