C 如何让LZO使用文件流?
我试图用LZO压缩一个文件流,但距离不远。具体地说,在提取由我的C 如何让LZO使用文件流?,c,file,compression,stream,lzo,C,File,Compression,Stream,Lzo,我试图用LZO压缩一个文件流,但距离不远。具体地说,在提取由我的compressFileWithLzo1x函数创建的存档文件时,我遇到了一个分段错误 我的main函数和原型声明如下: #include <stdio.h> #include <stdlib.h> #include "lzo/include/lzo/lzo1x.h" #define LZO_IN_CHUNK (128*1024L) #define LZO_OUT_CHUNK (LZO_IN_CHUNK +
compressFileWithLzo1x
函数创建的存档文件时,我遇到了一个分段错误
我的main
函数和原型声明如下:
#include <stdio.h>
#include <stdlib.h>
#include "lzo/include/lzo/lzo1x.h"
#define LZO_IN_CHUNK (128*1024L)
#define LZO_OUT_CHUNK (LZO_IN_CHUNK + LZO_IN_CHUNK/16 + 64 + 3)
int compressFileWithLzo1x(const char *inFn, const char *outFn);
int extractFileWithLzo1x(const char *inFn);
int main(int argc, char **argv) {
const char *inFilename = "test.txt";
const char *outFilename = "test.txt.lzo1x";
if ( compressFileWithLzo1x(inFilename, outFilename) != 0 )
exit(EXIT_FAILURE);
if ( extractFileWithLzo1x(outFilename) != 0 )
exit(EXIT_FAILURE);
return 0;
}
下面是我的解压功能的实现:
int compressFileWithLzo1x(const char *inFn, const char *outFn) {
FILE *inFnPtr = fopen(outFn, "r");
FILE *outFnPtr = fopen(outFn, "wb");
int compressionResult;
lzo_bytep in;
lzo_bytep out;
lzo_voidp wrkmem;
lzo_uint out_len;
size_t inResult;
if (lzo_init() != LZO_E_OK)
return -1;
in = (lzo_bytep)malloc(LZO_IN_CHUNK);
out = (lzo_bytep)malloc(LZO_OUT_CHUNK);
wrkmem = (lzo_voidp)malloc(LZO1X_1_MEM_COMPRESS);
do {
inResult = fread(in, sizeof(lzo_byte), LZO_IN_CHUNK, inFnPtr);
if (inResult == 0)
break;
compressionResult = lzo1x_1_compress(in, LZO_IN_CHUNK, out, &out_len, wrkmem);
if ((out_len >= LZO_IN_CHUNK) || (compressionResult != LZO_E_OK))
return -1;
if (fwrite(out, sizeof(lzo_byte), (size_t)out_len, outFnPtr) != (size_t)out_len || ferror(outFnPtr))
return -1;
fflush(outFnPtr);
} while (!feof(inFnPtr) && !ferror(inFnPtr));
free(wrkmem);
free(out);
free(in);
fclose(inFnPtr);
fclose(outFnPtr);
return 0;
}
int extractFileWithLzo1x(const char *inFn) {
FILE *inFnPtr = fopen(inFn, "rb");
lzo_bytep in = (lzo_bytep)malloc(LZO_IN_CHUNK);
lzo_bytep out = (lzo_bytep)malloc(LZO_OUT_CHUNK);
int extractionResult;
size_t inResult;
lzo_uint new_length;
if (lzo_init() != LZO_E_OK)
return -1;
do {
new_length = LZO_IN_CHUNK;
inResult = fread(in, sizeof(lzo_byte), LZO_IN_CHUNK, inFnPtr);
extractionResult = lzo1x_decompress(out, LZO_OUT_CHUNK, in, &new_length, NULL);
if ((extractionResult != LZO_E_OK) || (new_length != LZO_IN_CHUNK))
return -1;
fprintf(stderr, "out: [%s]\n", (unsigned char *)out);
} while (!feof(inFnPtr) && (!ferror(inFnPtr));
free(in);
free(out);
fclose(inFnPtr);
return 0;
}
分段故障发生在以下位置:
extractionResult = lzo1x_decompress(out, LZO_OUT_CHUNK, in, &new_length, NULL);
这种方法有什么问题导致分割错误
我希望这次没有遗漏任何代码。如果需要添加更多信息,请随时通知我。提前感谢您的建议。您给出的代码不会编译(在
#defines
;infeptr
中的伪=
,而不是在各个地方的inFnPtr
等)。但是:
fread()
返回的实际数据量,这很可能小于LZO\u IN\u CHUNK
compressionResult = lzo1x_1_compress(in, LZO_IN_CHUNK, out, &out_len, wrkmem);
应该是
compressionResult = lzo1x_1_compress(in, inResult, out, &out_len, wrkmem);
extractionResult = lzo1x_decompress(in, inResult, out, &new_length, NULL);
(这不太可能是问题所在,但会在文件末尾添加虚假垃圾。)extractionResult = lzo1x_decompress(out, LZO_OUT_CHUNK, in, &new_length, NULL);
应该是
compressionResult = lzo1x_1_compress(in, inResult, out, &out_len, wrkmem);
extractionResult = lzo1x_decompress(in, inResult, out, &new_length, NULL);
您正在压缩独立块。LZO解压器需要压缩数据的字节长度,因为当它解码EOF时,它会检查是否已消耗所有输入字节(如果没有,则返回一个错误),因此您还需要存储每个压缩块的长度。因此,您需要更复杂的文件格式。例如:
# compressing, in python-like pseudocode
ifile = open("data", "rb")
ofile = open("data.mylzo", "wb")
input, input_len = ifile.read(65536)
while input_len > 0:
compressed, compressed_len = lzo1x(input, input_len)
compressed_len -= 1 # store len-1 of next block
if compressed_len < 65536 - 1:
ofile.write(compressed_len & 255) # be sure of endianess in file formats!
ofile.write(compressed_len >> 8)
ofile.write(compressed)
else:
ofile.write(255) # incompressible block stored it as-is (saves space & time).
ofile.write(255)
ofile.write(input)
input, input_len = ifile.read(65536)
ofile.close()
ifile.close()
# decompressing, in python-like pseudocode
ifile = open("data.mylzo", "rb")
ofile = open("data", "wb")
compressed_len_s = ifile.read(2)
while len(compressed_len_s) == 2:
compressed_len = (compressed_len_s[0] | (compressed_len_s[1] << 8)) + 1
if compressed_len == 65536:
ofile.write(ifile.read(65536)) # this can be done without copying
else:
compressed = ifile.read(compressed_len)
decompressed = lzo1x_decompress(compressed, compressed_len)
ofile.write(decompressed)
compressed_len_s = ifile.read(2)
ofile.close()
ifile.close()
#压缩,类似python的伪代码
ifile=打开(“数据”、“rb”)
ofile=open(“data.mylzo”、“wb”)
输入,输入长度=ifile.read(65536)
当输入长度>0时:
压缩,压缩长度=lzo1x(输入,输入长度)
压缩的_len-=1#存储下一个块的len-1
如果压缩长度<65536-1:
ofile.write(compressed_len&255)#确保文件格式的结尾!
ofile.write(压缩长度>>8)
ofile.write(压缩)
其他:
ofile.write(255)#不可压缩块按原样存储(节省空间和时间)。
ofile.write(255)
ofile.write(输入)
输入,输入长度=ifile.read(65536)
ofile.close()
ifile.close()
#解压缩,使用类似python的伪代码
ifile=open(“data.mylzo”、“rb”)
ofile=打开(“数据”、“wb”)
压缩长度=ifile.read(2)
而len(压缩的len)=2:
compressed_len=(compressed_len_s[0]|(compressed_len_s[1]我认为您在int compressFileWithLzo1x
中打开了错误的文件:
FILE *inFnPtr = fopen(outFn, "r");
应该是
FILE *inFnPtr = fopen(inFn, "r");
我认为越来越近,但是在调用lzo1x\u 1\u compress()
之前和之后执行fprintf()
语句(查看in
和out
缓冲区)表明文本数据没有被压缩。