tec::MemFile Class Reference

A byte buffer class with stream-like read/write semantics. More...

#include <tec_memfile.hpp>

Classes
struct	_Char2

Public Member Functions
	MemFile ()
	Constructs a buffer with the specified block size.
	MemFile (size_t block_size)
	Constructs a MemFile with a specified block size for preallocation.
	MemFile (const std::string &s)
	Constructs a MemFile from a std::string.
	MemFile (const void *src, size_t len)
	Constructs a MemFile from a raw memory buffer.
void	copy_from (const MemFile &src)
	Copies data from another MemFile instance.
void	move_from (MemFile &&src, size_t size_to_shrink=0)
	Moves data from another MemFile instance.
const std::string &	str () const noexcept
	Returns a const reference to the internal string buffer.
const void *	data () const
	Returns a const pointer to the buffer's data.
void *	data ()
	Returns a mutable pointer to the buffer's data.
const char *	ptr (long pos) const
	Returns a const pointer to a specific position in the buffer.
char *	ptr (long pos)
	Returns a mutable pointer to a specific position in the buffer.
constexpr size_t	block_size () const noexcept
	Returns the block size used for buffer expansion.
size_t	size () const noexcept
	Returns the logical size of the data in the buffer.
size_t	capacity () const noexcept
	Returns the current capacity of the underlying storage.
constexpr long	tell () const noexcept
	Returns the current read/write position.
constexpr void	rewind () noexcept
	Resets the read/write position to the beginning of the buffer.
long	seek (long offset, int whence)
	Moves the read/write position relative to a reference point.
void	resize (size_t len)
size_t	write (const void *src, size_t len)
	Writes data into the buffer at the current position.
size_t	read (void *dst, size_t len)
	Reads data from the buffer starting at the current position.
std::string	as_hex () const
	Returns a human-readable hex+ASCII dump string.

Static Public Member Functions
static constexpr _Char2	to_hex_chars (unsigned char ch) noexcept
	Converts a byte to a 2-character representation suitable for hex dumps.

Static Public Attributes
static constexpr size_t	kDefaultBlockSize {BUFSIZ}
	Default block size for buffer expansion, matches BUFSIZ from <stdio.h>. Usually 8192 bytes.

Detailed Description

A byte buffer class with stream-like read/write semantics.

The MemFile class provides a dynamically resizing buffer for sequential reading and writing of elements of type char. It mimics the behavior of file streams using seek, tell, read, and write operations. The buffer grows in blocks of a configurable size to minimize reallocations.

Constructor & Destructor Documentation

MemFile() [1/4]

tec::MemFile::MemFile ( )

inline

Constructs a buffer with the specified block size.

The initial capacity is set to one block. The buffer starts empty with position at 0.

Parameters

block_size

Size of each growth block. Must be greater than 0. Defaults to kDefaultBlockSize.

MemFile() [2/4]

tec::MemFile::MemFile ( size_t  block_size )

inlineexplicit

Constructs a MemFile with a specified block size for preallocation.

Initializes the internal buffer with the given block size as capacity, but sets the initial size to 0. This allows for efficient appending without frequent reallocations.

Parameters

block_size

The initial capacity and block size for allocation.

MemFile() [3/4]

tec::MemFile::MemFile ( const std::string &  s )

inlineexplicit

Constructs a MemFile from a std::string.

Uses a default block size for allocation and writes the contents of the provided string into the buffer.

Parameters

s	The string to initialize the buffer with.

MemFile() [4/4]

tec::MemFile::MemFile ( const void *  src, size_t  len  )

inline

Constructs a MemFile from a raw memory buffer.

Uses a default block size for allocation and writes the specified length of data from the source pointer into the buffer.

Parameters

src	Pointer to the source data.
len	Length of the data to copy.

Member Function Documentation

as_hex()

std::string tec::MemFile::as_hex ( ) const

inline

Returns a human-readable hex+ASCII dump string.

Each byte is represented by exactly two characters:

• Printable ASCII characters in the range 0x21–0x7E (! to ~) are shown as space + the character itself.
• All other bytes (including space 0x20, control characters, DEL, and values ≥ 0x7F) are shown as two uppercase hexadecimal digits.

This format is extremely useful for debugging binary data, network packets, or memory contents, because it makes text-like regions immediately recognizable while still showing exact byte values.

Returns

std::string A string of length exactly 2 * size(), containing the mixed hex/ASCII representation.

Complexity

O(N) where N = size(), with a very tight constant factor.

Example

const char hello[] = "Hello\x01\x02World\xFF\0";
MemFile data(hello, strlen(hello));
// data contains: 48 65 6C 6C 6F 01 02 57 6F 72 6C 64 FF
std::cout << data.as_hex() << '\n';
// Output: " H e l l o010203 W o r l dFF"

Note

Space (0x20) is deliberately rendered as hex "20", not as ' ' + ' ', which matches classic hex dump tools and avoids ambiguity.

See also

to_hex_chars()

block_size()

constexpr size_t tec::MemFile::block_size ( ) const

inlineconstexprnoexcept

Returns the block size used for buffer expansion.

Returns

The current block size in number of elements.

capacity()

size_t tec::MemFile::capacity ( ) const

inlinenoexcept

Returns the current capacity of the underlying storage.

Returns

Total number of bytes the buffer can hold without reallocation.

copy_from()

void tec::MemFile::copy_from ( const MemFile &  src )

inline

Copies data from another MemFile instance.

Rewinds the current position and writes the entire contents of the source MemFile into this one.

Parameters

src	The source MemFile to copy from.

data() [1/2]

void * tec::MemFile::data ( )

inline

Returns a mutable pointer to the buffer's data.

Assumes the buffer is non-empty; uses at(0) to access, which may throw if empty. This avoids certain compiler warnings related to empty strings.

Returns

Mutable pointer to the data.

data() [2/2]

const void * tec::MemFile::data ( ) const

inline

Returns a const pointer to the buffer's data.

Assumes the buffer is non-empty; uses at(0) to access, which may throw if empty. This avoids certain compiler warnings related to empty strings.

Returns

Const pointer to the data.

move_from()

void tec::MemFile::move_from ( MemFile &&  src, size_t  size_to_shrink = 0  )

inline

Moves data from another MemFile instance.

Transfers ownership of the buffer and state from the source, optionally shrinking the buffer to a specified size if smaller than the current size.

Parameters

src	The rvalue reference to the source MemFile.
size_to_shrink	Optional size to resize the buffer to (default 0, no shrink).

ptr() [1/2]

char * tec::MemFile::ptr ( long  pos )

inline

Returns a mutable pointer to a specific position in the buffer.

No bounds checking is performed; caller must ensure pos is valid.

Parameters

pos	The position offset.

Returns

Mutable pointer to the position.

ptr() [2/2]

const char * tec::MemFile::ptr ( long  pos ) const

inline

Returns a const pointer to a specific position in the buffer.

No bounds checking is performed; caller must ensure pos is valid.

Parameters

pos	The position offset.

Returns

Const pointer to the position.

read()

size_t tec::MemFile::read ( void *  dst, size_t  len  )

inline

Reads data from the buffer starting at the current position.

Does not read past the logical end of data (size_).

Parameters

dst	Pointer to the destination buffer.
len	Maximum number of elements to read.

Returns

Number of elements actually read. Returns 0 if at end of data or if len == 0 or no data.

seek()

long tec::MemFile::seek ( long  offset, int  whence  )

inline

Moves the read/write position relative to a reference point.

Behaves like fseek. Supports SEEK_SET, SEEK_CUR, and SEEK_END.

Parameters

offset	Number of elements to move (can be negative).
whence	Reference point: SEEK_SET: from beginning of buffer SEEK_CUR: from current position SEEK_END: from end of data

Returns

A new read/write position, -1 if seeking before start, -2 if seeking beyond end.

size()

size_t tec::MemFile::size ( ) const

inlinenoexcept

Returns the logical size of the data in the buffer.

This is the amount of data that has been written and is readable.

Returns

Number of bytes currently stored.

str()

const std::string & tec::MemFile::str ( ) const

inlinenoexcept

Returns a const reference to the internal string buffer.

Returns

Const reference to the buffer.

tell()

constexpr long tec::MemFile::tell ( ) const

inlineconstexprnoexcept

Returns the current read/write position.

Returns

The current position as a signed offset from the start.

to_hex_chars()

static constexpr _Char2 tec::MemFile::to_hex_chars ( unsigned char  ch )

inlinestaticconstexprnoexcept

Converts a byte to a 2-character representation suitable for hex dumps.

Returns a 2-element struct containing either:

• The two hexadecimal digits (uppercase) representing the byte value, or
• The literal ASCII character preceded by a space, but only for printable ASCII characters in the range 0x21–0x7E (! to ~). Space (0x20) is deliberately treated as non-printable and rendered in hex.

This format is commonly used in classic hex dump tools (e.g. hexdump -C, xxd, debug output) where printable characters are shown directly and everything else in hex.

Parameters

value

The byte to convert.

Returns

struct _Char2 A struct with two characters:

• For printable ASCII (except space): ‘{ ’ ', actual_char }
• For all other values (including space, control chars, and high bytes):{ '0'..'F', '0'..'F' }`

Examples

to_hex_chars(65);   // 'A'  → {' ', 'A'}
to_hex_chars(32);   // ' '  → {'2', '0'}   (space is forced to hex)
to_hex_chars(10);   // '\n' → {'0', 'A'}
to_hex_chars(255);  // 0xFF → {'F', 'F'}

Note

The function is constexpr and inline, making it usable in both runtime and compile-time contexts with zero overhead.

See also

as_hex()

write()

size_t tec::MemFile::write ( const void *  src, size_t  len  )

inline

Writes data into the buffer at the current position.

The buffer automatically expands if necessary. Expansion occurs in multiples of blk_size_ to reduce reallocations.

Parameters

src	Pointer to the source data.
len	Number of elements to write.

Returns

Number of elements actually written. Returns 0 on failure (e.g., out of memory or len == 0).

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The documentation for this class was generated from the following file:

• tec_memfile.hpp