このzlib文字列圧縮解除で何が問題になっていますか？

Question

私のアプリケーションのための単純な文字列圧縮アルゴリズムを作成しようとしています。

/* 
Decompresses the source buffer into the destination buffer. sourceLen is 
the byte length of the source buffer. Upon entry, destLen is the total size 
of the destination buffer, which must be large enough to hold the entire 
uncompressed data. (The size of the uncompressed data must have been saved 
previously by the compressor and transmitted to the decompressor by some 
mechanism outside the scope of this compression library.) Upon exit, destLen 
is the actual size of the uncompressed buffer. 

uncompress returns Z_OK if success, Z_MEM_ERROR if there was not 
enough memory, Z_BUF_ERROR if there was not enough room in the output 
buffer, or Z_DATA_ERROR if the input data was corrupted or incomplete. 
*/ 

[Base64 initialize]; 
NSData * data = [Base64 decode:@"MDAwMDAwNTB42vPMVkhKzVNIBeLsnNTMPB0IpVCWWZyVqpAJkalKTVUoS8xTSMpJLC0HALWrEYi="]; 

NSString * deBase64 = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding]; 

int lengteOP = [[deBase64 substringWithRange:NSMakeRange(0,8)] intValue]; 
NSUInteger lengteIP = [deBase64 length]; 

const unsigned char *input = (const unsigned char *) [[deBase64 substringFromIndex:8] cStringUsingEncoding:NSASCIIStringEncoding]; 
unsigned char * dest; 

uncompress(dest, lengteOP, input, lengteIP); 

これを試すと、EXC_BADD_ACCESSエラーが発生します。 文字列がiPhoneのSDK

におけるライブラリと同じZLIBを使用デルファイのコードで構築され、そのZLIB-ED文字列に続く文字列の長さを表す最初の8つの文字をbase64でエンコードストリング。

Answer 1

私はコードを実行しませんでしたが、あなたの問題はdestである可能性があります。ここでは、ドキュメントの抜粋です。エントリ時

、destlenをは 全体の非圧縮データを保持するのに十分な大きさでなければならない宛先バッファの合計サイズ 、です。

先は、関数を呼び出す前に割り当てられたメモリを持っている必要があり、それ以外の場合はEXC_BAD_ACCESSを引き起こし、無効なメモリにデータを書き込むしようとします。

次のことを試してみてください。

unsigned char * dest = malloc(sizeof(unsigned char) * lengteOP); 

uncompress(dest, lengteOP, input, lengteIP); 

//Use dest (create NSString with proper encoding for example) 

free(dest); 

Answer 2

- 完成したコード

/* 
Decompresses the source buffer into the destination buffer. sourceLen is 
the byte length of the source buffer. Upon entry, destLen is the total size 
of the destination buffer, which must be large enough to hold the entire 
uncompressed data. (The size of the uncompressed data must have been saved 
previously by the compressor and transmitted to the decompressor by some 
mechanism outside the scope of this compression library.) Upon exit, destLen 
is the actual size of the uncompressed buffer. 

uncompress returns Z_OK if success, Z_MEM_ERROR if there was not 
enough memory, Z_BUF_ERROR if there was not enough room in the output 
buffer, or Z_DATA_ERROR if the input data was corrupted or incomplete. 

ZEXTERN int ZEXPORT uncompress OF((Bytef *dest, uLongf *destLen, 
const Bytef *source, uLong sourceLen)); 

*/ 

[Base64 initialize]; 
NSData * data = [Base64 decode:@"MDAwMDAwNTB42vPMVkhKzVNIBeLsnNTMPB0IpVCWWZyVqpAJkalKTVUoS8xTSMpJLC0HALWrEYi="]; 

NSString * deBase64 = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding]; 

uLongf lengthOriginal = [[deBase64 substringWithRange:NSMakeRange(0,8)] floatValue]; 
uLongf * lengteOP = malloc(sizeof(uLongf)); 

lengteOP = &lengthOriginal; 

NSUInteger lengteIP = [deBase64 length]; 

NSString * codedString = [deBase64 substringFromIndex:8]; 

const unsigned char *input = (const unsigned char *) [codedString cStringUsingEncoding:NSISOLatin1StringEncoding]; 

unsigned char * dest = malloc((sizeof(unsigned char) * lengthOriginal)); 

uncompress(dest, lengteOP, input, lengteIP); 

NSString * bla = @"Decoded string :"; 
NSLog([bla stringByAppendingString:[NSString stringWithCString:dest encoding:NSASCIIStringEncoding]]); 



free(dest); 
free(lengteOP);