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update simple_buffer example

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there were a few tiny inaccuracies, especially in error conditions.
This commit is contained in:
Yann Collet 2019-06-06 14:17:44 -07:00
parent 1d759576b9
commit 798301b4e1
1 changed files with 25 additions and 20 deletions
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45
examples/simple_buffer.c
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@ -3,18 +3,18 @@
* 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_safe. Both of these are documented in
* the lz4.h header file; I recommend reading them.
* The functions you'll likely want are LZ4_compress_default and LZ4_decompress_safe.
* 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.
/* Dependencies */
#include <stdio.h> // For printf()
#include <string.h> // For memcmp()
#include <stdlib.h> // For exit()
#include "lz4.h" // This is all that is required to expose the prototypes for basic compression and decompression.
/*
* Easy show-error-and-bail function.
* Simple show-error-and-bail function.
*/
void run_screaming(const char* message, const int code) {
printf("%s \n", message);
@ -32,9 +32,9 @@ int main(void) {
// 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).
// This is baked into the API and not going to change, for consistency.
// If your program uses different pointer types,
// you may need to do some casting or set the right -Wno 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.
@ -44,7 +44,7 @@ int main(void) {
// 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);
char* compressed_data = malloc((size_t)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.
@ -52,21 +52,26 @@ int main(void) {
// Save the return value for error checking.
const int compressed_data_size = LZ4_compress_default(src, compressed_data, src_size, max_dst_size);
// Check return_value to determine what happened.
if (compressed_data_size < 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.", compressed_data_size);
if (compressed_data_size == 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 (compressed_data_size <= 0)
run_screaming("A 0 or negative result from LZ4_compress_default() indicates a failure trying to compress the data. ", 1);
if (compressed_data_size > 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.
compressed_data = (char *)realloc(compressed_data, compressed_data_size);
compressed_data = (char *)realloc(compressed_data, (size_t)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.
// Now that we've successfully compressed the information from *src to *compressed_data, let's do the opposite!
// The decompression will need to know the compressed size, and an upper bound of the decompressed size.
// In this example, we just re-use this information from previous section,
// but in a real-world scenario, metadata must be transmitted to the decompression side.
// Each implementation is in charge of this part. Oftentimes, it adds some header of its own.
// Sometimes, the metadata can be extracted from the local context.
// First, let's create a *new_src location of size src_size since we know that value.
char* const regen_buffer = malloc(src_size);
if (regen_buffer == NULL)
run_screaming("Failed to allocate memory for *regen_buffer.", 1);
@ -77,17 +82,17 @@ int main(void) {
free(compressed_data); /* no longer useful */
if (decompressed_size < 0)
run_screaming("A negative result from LZ4_decompress_safe indicates a failure trying to decompress the data. See exit code (echo $?) for value returned.", decompressed_size);
if (decompressed_size == 0)
run_screaming("I'm not sure this function can ever return 0. Documentation in lz4.h doesn't indicate so.", 1);
if (decompressed_size > 0)
if (decompressed_size >= 0)
printf("We successfully decompressed some data!\n");
// Not only does a positive return value mean success,
// value returned == number of bytes regenerated from compressed_data stream.
if (decompressed_size != src_size)
run_screaming("Decompressed data is different from original! \n", 1);
/* Validation */
// We should be able to compare our original *src with our *new_src and be byte-for-byte identical.
if (memcmp(src, regen_buffer, 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", regen_buffer);
printf("Validation done. The string we ended up with is:\n%s\n", regen_buffer);
return 0;
}