Configuration & Compile-Time Flags

minipaxtar is designed to be lean and adaptable for embedded environments, bare-metal kernels, and resource-constrained platforms. You can tailor its feature set, binary footprint, and dependencies using preprocessor definitions.

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High-Level Feature Switches

These macros control major API subsets and platform capability dependencies.

Preprocessor Flag	Default	Description
MPTAR_NO_READ	Undefined	Disables the reading and parsing API (mptar_reader, mptar_read_header, mptar_read_data_chunk, etc.). Reduces binary footprint when only writing archives.
MPTAR_NO_WRITE	Undefined	Disables the archive creation API (mptar_writer, mptar_write_header, mptar_write_data_chunk, etc.). Reduces binary footprint when only extracting archives.
MPTAR_SUPPORT_SPECIAL	Undefined / ON in CMake	Include support for special node metadata (devmajor and devminor device numbers).
MPTAR_SUPPORT_EXTRA_TIMES	Undefined / ON in CMake	Include support for extended PAX timestamp attributes (atime access time and ctime change time).

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Detailed Switch Usage

1. Stripping Read or Write API

If your application only needs to unpack archives or only needs to create them, you can strip the unused logic entirely:

#define MPTAR_NO_READ
#include "minipaxtar.h"

gcc -DMPTAR_NO_WRITE -c minipaxtar.c -o minipaxtar.o

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2. Extended Metadata Features

By default, minipaxtar doesn't define any compilation options, however it enables support on cmake for special device nodes and extended PAX timestamps. If your system does not require these metadata fields, you can omit them to simplify mptar_metadata structs and handling logic.

• MPTAR_SUPPORT_SPECIAL: Includes device node fields (meta.devmajor and meta.devminor).
• MPTAR_SUPPORT_EXTRA_TIMES: Includes extended access time (meta.atime) and change time (meta.ctime).

#ifdef MPTAR_SUPPORT_SPECIAL
    printf("Device major: %u, minor: %u\n", meta.devmajor, meta.devminor);
#endif

#ifdef MPTAR_SUPPORT_EXTRA_TIMES
    printf("Access time: %llu, Change time: %llu\n", meta.atime, meta.ctime);
#endif

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Custom Number Conversion Hooks

To prevent dependencies on Standard C library functions like snprintf or strtoull, minipaxtar ships with internal fallback functions for integer-to-string and string-to-integer conversions.

If your environment provides optimized, custom, or assembly-accelerated equivalents, define these macros to omit built-in implementations and delegate to external routines of the same name:

Flag	Omitted Built-in	Required extern Function Signature
MPTAR_CUSTOM_U64TOA	mptar_u64toa	char* mptar_u64toa(mptar_uint64 value, char* str, mptar_size_t str_size, int *out_err);
MPTAR_CUSTOM_I64TOA	mptar_i64toa	char* mptar_i64toa(mptar_int64 value, char* buf, mptar_size_t buf_size, int *out_err);
MPTAR_CUSTOM_ATOU64	mptar_atou64	mptar_uint64 mptar_atou64(const char* str, mptar_size_t len, int* err);
MPTAR_CUSTOM_ATOI64	mptar_atoi64	mptar_int64 mptar_atoi64(const char* str, mptar_size_t len, int* err);

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Example: Supplying Custom Conversion Hooks

When defining any of the custom conversion flags, ensure your custom implementations are declared or linked in your binary:

/* Enable custom unsigned 64-bit conversion hook */
#define MPTAR_CUSTOM_ATOU64
#include "minipaxtar.h"

/* Supply the external function matching the exact name and signature */
uint64_t mptar_atou64(const char* str, mptar_size_t len, int* err) {
    /* Custom optimized conversion logic */
    uint64_t result = 0;
    /* ... */
    if (err) *err = MPTAR_OK; /* or 0 */
    return result;
}

CMake Integration Example

If building via CMake, you can toggle these definitions cleanly using target_compile_definitions() or CMake option()s:

# Disable write support and use custom 64-bit parser
target_compile_definitions(my_app PRIVATE
    MPTAR_NO_WRITE
    MPTAR_CUSTOM_ATOU64
)