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/*
* basics.c
* Copyright : Kyle Harper
* License : Follows same licensing as the lz4.c/lz4.h program at any given time. Currently, BSD 2.
* Description: Example program to demonstrate the basic usage of the compress/decompress functions within lz4.c/lz4.h.
* The functions you'll likely want are LZ4_compress_default and LZ4_decompress_fast. Both of these are documented in
* the lz4.h header file; I recommend reading them.
*/
/* Includes, for Power! */
#include "lz4.h" // This is all that is required to expose the prototypes for basic compression and decompression.
#include <stdio.h> // For printf()
#include <string.h> // For memcmp()
#include <stdlib.h> // For exit()
/*
* Easy show-error-and-bail function.
*/
void run_screaming(const char *message, const int code) {
printf("%s\n", message);
exit(code);
return;
}
/*
* main
*/
int main(void) {
/* Introduction */
// Below we will have a Compression and Decompression section to demonstrate. There are a few important notes before we start:
// 1) The return codes of LZ4_ functions are important. Read lz4.h if you're unsure what a given code means.
// 2) LZ4 uses char* pointers in all LZ4_ functions. This is baked into the API and probably not going to change. If your
// program uses pointers that are unsigned char*, void*, or otherwise different you may need to do some casting or set the
// right -W compiler flags to ignore those warnings (e.g.: -Wno-pointer-sign).
/* Compression */
// We'll store some text into a variable pointed to by *src to be compressed later.
const char *src = "Lorem ipsum dolor sit amet, consectetur adipiscing elit.";
// The compression function needs to know how many bytes of data we're sending. The string above has 57 characters == 57 bytes.
const int src_size = 57;
// LZ4 provides a function that will tell you the maximum size of compressed output based on input data via LZ4_compressBound().
const int max_dst_size = LZ4_compressBound(src_size);
// We will use that size for our destination boundary when allocating space.
char *compressed_data = malloc(max_dst_size);
if (compressed_data == NULL)
run_screaming("Failed to allocate memory for *compressed_data.", 1);
// That's all the information and preparation LZ4 needs to compress *src into *compressed_data. Invoke LZ4_compress_default now
// with our size values and pointers to our memory locations. Save the return value for error checking.
int return_value = 0;
return_value = LZ4_compress_default(src, compressed_data, src_size, max_dst_size);
// Check return_value to determine what happened.
if (return_value < 0)
run_screaming("A negative result from LZ4_compress_default indicates a failure trying to compress the data. See exit code (echo $?) for value returned.", return_value);
if (return_value == 0)
run_screaming("A result of 0 means compression worked, but was stopped because the destination buffer couldn't hold all the information.", 1);
if (return_value > 0)
printf("We successfully compressed some data!\n");
// Not only does a positive return_value mean success, the value returned == the number of bytes required. You can use this to
// realloc() *compress_data to free up memory, if desired. We'll do so just to demonstrate the concept.
const int compressed_data_size = return_value;
compressed_data = (char *)realloc(compressed_data, compressed_data_size);
if (compressed_data == NULL)
run_screaming("Failed to re-alloc memory for compressed_data. Sad :(", 1);
/* Decompression */
// Now that we've successfully compressed the information from *src to *compressed_data, let's do the opposite! We'll create a
// *new_src location of size src_size since we know that value.
char *new_src = malloc(src_size);
if (new_src == NULL)
run_screaming("Failed to allocate memory for *new_src.", 1);
// The LZ4_decompress_fast function needs to know where the compressed data is, where the new_src memory location is, and how
// large the new_src (uncompressed) output will be. Again, save the return_value.
return_value = LZ4_decompress_fast(compressed_data, new_src, src_size);
if (return_value < 0)
run_screaming("A negative result from LZ4_decompress_fast indicates a failure trying to decompress the data. See exit code (echo $?) for value returned.", return_value);
if (return_value == 0)
run_screaming("I'm not sure this function can ever return 0. Documentation in lz4.h doesn't indicate so.", 1);
if (return_value > 0)
printf("We successfully decompressed some data!\n");
// Not only does a positive return value mean success, the value returned == the number of bytes read from the compressed_data
// stream. I'm not sure there's ever a time you'll need to know this in most cases...
/* Validation */
// We should be able to compare our original *src with our *new_src and be byte-for-byte identical.
if (memcmp(src, new_src, src_size) != 0)
run_screaming("Validation failed. *src and *new_src are not identical.", 1);
printf("Validation done. The string we ended up with is:\n%s\n", new_src);
return 0;
}
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