c and objective-c -- const char* and char* - objective-c

I have a function:
-(void)ADPCMDecode:(char *)indata : (short *)outdata :(long)len {
indata is a char and the function does pointer arithmetic to iterate for a length of len, modifying outdata, which is a short and I will need to do pointer arithmetic to get the values from it.
I am attempting to call the function using:
const char *modulatedBytes1 = [modulatedAudio bytes];
char *modulatedBytes [] = modulatedBytes1;
unsigned int moduleatedLength = [modulatedAudio length];
short *decompressedBytes = NULL;
[self ADPCMDecode:modulatedBytes :decompressedBytes :moduleatedLength];
DLog(#"%hi",decompressedBytes[1]);
I get a BAD ACCESS error on this line: *outp++ = valprev; within the function, because I am passing a constant char * instead of a char *
How should I call the function, and how would I get the output from it?
I have no background in C, which is why I do not understand how to go about doing this.
Here is the C only version of the same question:
https://pastee.org/d3y3z

Related

How do you convert FString into Char* ? UE4

const char* bufmessage = PlayerLocation;
int sendOK = sendto(out, bufmessage, strlen(bufmessage), 0, (sockaddr*)&server, sizeof(server));
no suitable conversion for FString to const char*

A 1 line solution to convert from some FString to char* would be this:
// Assuming you have some FString myFString created e.g., with TEXT("Some FString")
char* result = TCHAR_TO_ANSI(*myFString);
Note: As the comments point out, this assumes the FString will not go out of scope.

How can I transfer data from unsigned char * to char * safely?

I am willing to transfer data from unsigned char hash[512 + 1] to char res[512 + 1] safely.
My C hashing library MHASH returns a result so it can be printed as listed below.
for (int i = 0; i < size /*hash block size*/; i++)
printf("%.2x", hash[i]); // which is unsigned char - it prints normal hash characters in range [a-z,0-9]
printf("\n");
I am willing to do something like that (see below).
const char* res = (const char *)hash; // "hash" to "res"
printf("%s\n", res); // print "res" (which is const char*) - if i do this, unknown characters are printed
I know the difference between char and unsigned char, but I don't know how to transfer data. Any answer would be greatly appreciated, thanks in advance. But please do not recommend me C++ (STD) code, I am working on a project that is not STD-linked.

Given that the contents of the unsigned char array are printable characters, you can always safely convert it to char. Either a hardcopy with memcpy or a pointer reference as in the code you have already written.
I'm guessing that the actual problem here is that the unsigned char array contents are not actually printable characters, but integers in some format. You'll have to convert them from integer to ASCII letters. How to do this depends on the format of the data, which isn't clear in your question.

Assuming the following:
#define ARR_SIZE (512 + 1)
unsigned char hash[ARR_SIZE];
char res[ARR_SIZE];
/* filling up hash here. */
Just do:
#include <string.h>
...
memcpy(res, hash, ARR_SIZE);

Well, thank you guys for your answers, but unfortunately nothing worked yet. I am now sticking with the code below.
char res[(sizeof(hash) * 2) + 1] = { '\0' };
char * pPtr = res;
for (int i = 0; i < hashBlockSize; i++)
sprintf(pPtr + (i * 2), "%.2x", hash[i]);
return (const char *)pPtr;
Until there is any other much more performant way to get this done. It's right, my question is strongly related to MHASH Library.

XOR reverse a string in objective-c get an error

I want to use the following code to reverse a char * type string in objective-c:
- (char *)reverseString:(char *)aString
{
unsigned long length = strlen(aString);
int end = length - 1;
int start = 0;
while (start < end) {
aString[start] ^= aString[end];
aString[end] ^= aString[start];
aString[start] ^= aString[end];
++start;
--end;
}
return aString;
}
But I got an error EXC_BAD_ACCESS at this line
aString[start] ^= aString[end]
I googled and found people said I can't modify a literal string because it is readonly. I am new to C so I wonder what simple data type (no object) I can use in this example? I get the same error when I use (char []) aString to replace (char *) aString.

I assume you're calling this like
[myObj reverseString:"foobar"];
The string "foobar" here is a constant literal string. Its type should be const char *, but because C is braindead, it's char *. But it's still constant, so any attempt to modify it is going to fail.
Declaring the method as taking char[] actually makes no difference whatsoever. When used as a parameter type, char[] is identical to char*.
You have two choices here. The first is to duplicate the string before passing it to the method. The second is to change the method to not modify its input string at all but instead to return a new string as output. Both can be accomplished using strdup(). Just remember that the string returned from strdup() will need to be free()'d later.

How to interpret objective-c type specifier (e.g. returned by method_copyReturnType())?

Given I have a type specifier as returned by method_copyReturnType(). In the GNU runtime delivered with the GCC there are various methods to work with such a type specifier like objc_sizeof_type(), objc_alignof_type() and others.
When using the Apple runtime there are no such methods.
How can I interpret a type specifier string (e.g. get the size of a type) using the Apple runtime without implementing an if/else or case switch for myself?
[update]
I am not able to use the Apple Foundation.

I believe that you're looking for NSGetSizeAndAlignment:
Obtains the actual size and the aligned size of an encoded type.
const char * NSGetSizeAndAlignment (
const char *typePtr,
NSUInteger *sizep,
NSUInteger *alignp
);
Discussion
Obtains the actual size and the aligned size of the first data type represented by typePtr and returns a pointer to the position of the next data type in typePtr.
This is a Foundation function, not part of the base runtime, which is probably why you didn't find it.
UPDATE: Although you didn't initially mention that you're using Cocotron, it is also available there. You can find it in Cocotron's Foundation, in NSObjCRuntime.m.
Obviously, this is much better than rolling your own, since you can trust it to always correctly handle strings generated by its own runtime in the unlikely event that the encoding characters should change.
For some reason, however, it's unable to handle the digit elements of a method signature string (which presumably have something to do with offsets in memory). This improved version, by Mike Ash will do so:
static const char *SizeAndAlignment(const char *str, NSUInteger *sizep, NSUInteger *alignp, int *len)
{
const char *out = NSGetSizeAndAlignment(str, sizep, alignp);
if(len)
*len = out - str;
while(isdigit(*out))
out++;
return out;
}

afaik, you'll need to bake that info into your binary. just create a function which returns the sizeof and alignof in a struct, supports the types you must support, then call that function (or class method) for the info.
The program below shows you that many of the primitives are just one character. So the bulk of the function's implementation could be a switch.
static void test(SEL sel) {
Method method = class_getInstanceMethod([NSString class], sel);
const char* const type = method_copyReturnType(method);
printf("%s : %s\n", NSStringFromSelector(sel).UTF8String, type);
free((void*)type);
}
int main(int argc, char *argv[]) {
#autoreleasepool {
test(#selector(init));
test(#selector(superclass));
test(#selector(isEqual:));
test(#selector(length));
return 0;
}
}
and you could then use this as a starting point:
typedef struct t_pair_alignof_sizeof {
size_t align;
size_t size;
} t_pair_alignof_sizeof;
static t_pair_alignof_sizeof MakeAlignOfSizeOf(size_t align, size_t size) {
t_pair_alignof_sizeof ret = {align, size};
return ret;
}
static t_pair_alignof_sizeof test2(SEL sel) {
Method method = class_getInstanceMethod([NSString class], sel);
const char* const type = method_copyReturnType(method);
const size_t length = strlen(type);
if (1U == length) {
switch (type[0]) {
case '#' :
return MakeAlignOfSizeOf(__alignof__(id), sizeof(id));
case '#' :
return MakeAlignOfSizeOf(__alignof__(Class), sizeof(Class));
case 'c' :
return MakeAlignOfSizeOf(__alignof__(signed char), sizeof(signed char));
...

How to do CRC32 hashing on a string in objective C

as per title, i couldnt find another tutorial on this...
i found a piece of code here: http://classroomm.com/objective-c/index.php?action=printpage;topic=2891.0
but it is giving me alot of warnings and doesnt really know how to use it.
Any other solution?

You might want to check this out - http://code.google.com/p/ofc/wiki/DCRC32

Just use crc32() function, it's simple and straight forward. See this answer for details: https://stackoverflow.com/a/14533955/1760595

I modified http://www.csbruce.com/software/crc32.c slightly,
and used UTF8String method to get a pointer to the internal CString representation of NSString.
This saves copying.
Unfotunately zlib's crc32 implementation needs a buffer length.
This one just terminates with the 0 byte at the end of the C-String.
#implementation NSString (crc32)
static unsigned long Crc32_String(const char *string)
{
static const unsigned long crcTable[256] = {
0x00000000,0x77073096,0xEE0E612C,0x990951BA,0x076DC419,0x706AF48F,0xE963A535,
0x9E6495A3,0x0EDB8832,0x79DCB8A4,0xE0D5E91E,0x97D2D988,0x09B64C2B,0x7EB17CBD,
0xE7B82D07,0x90BF1D91,0x1DB71064,0x6AB020F2,0xF3B97148,0x84BE41DE,0x1ADAD47D,
0x6DDDE4EB,0xF4D4B551,0x83D385C7,0x136C9856,0x646BA8C0,0xFD62F97A,0x8A65C9EC,
0x14015C4F,0x63066CD9,0xFA0F3D63,0x8D080DF5,0x3B6E20C8,0x4C69105E,0xD56041E4,
0xA2677172,0x3C03E4D1,0x4B04D447,0xD20D85FD,0xA50AB56B,0x35B5A8FA,0x42B2986C,
0xDBBBC9D6,0xACBCF940,0x32D86CE3,0x45DF5C75,0xDCD60DCF,0xABD13D59,0x26D930AC,
0x51DE003A,0xC8D75180,0xBFD06116,0x21B4F4B5,0x56B3C423,0xCFBA9599,0xB8BDA50F,
0x2802B89E,0x5F058808,0xC60CD9B2,0xB10BE924,0x2F6F7C87,0x58684C11,0xC1611DAB,
0xB6662D3D,0x76DC4190,0x01DB7106,0x98D220BC,0xEFD5102A,0x71B18589,0x06B6B51F,
0x9FBFE4A5,0xE8B8D433,0x7807C9A2,0x0F00F934,0x9609A88E,0xE10E9818,0x7F6A0DBB,
0x086D3D2D,0x91646C97,0xE6635C01,0x6B6B51F4,0x1C6C6162,0x856530D8,0xF262004E,
0x6C0695ED,0x1B01A57B,0x8208F4C1,0xF50FC457,0x65B0D9C6,0x12B7E950,0x8BBEB8EA,
0xFCB9887C,0x62DD1DDF,0x15DA2D49,0x8CD37CF3,0xFBD44C65,0x4DB26158,0x3AB551CE,
0xA3BC0074,0xD4BB30E2,0x4ADFA541,0x3DD895D7,0xA4D1C46D,0xD3D6F4FB,0x4369E96A,
0x346ED9FC,0xAD678846,0xDA60B8D0,0x44042D73,0x33031DE5,0xAA0A4C5F,0xDD0D7CC9,
0x5005713C,0x270241AA,0xBE0B1010,0xC90C2086,0x5768B525,0x206F85B3,0xB966D409,
0xCE61E49F,0x5EDEF90E,0x29D9C998,0xB0D09822,0xC7D7A8B4,0x59B33D17,0x2EB40D81,
0xB7BD5C3B,0xC0BA6CAD,0xEDB88320,0x9ABFB3B6,0x03B6E20C,0x74B1D29A,0xEAD54739,
0x9DD277AF,0x04DB2615,0x73DC1683,0xE3630B12,0x94643B84,0x0D6D6A3E,0x7A6A5AA8,
0xE40ECF0B,0x9309FF9D,0x0A00AE27,0x7D079EB1,0xF00F9344,0x8708A3D2,0x1E01F268,
0x6906C2FE,0xF762575D,0x806567CB,0x196C3671,0x6E6B06E7,0xFED41B76,0x89D32BE0,
0x10DA7A5A,0x67DD4ACC,0xF9B9DF6F,0x8EBEEFF9,0x17B7BE43,0x60B08ED5,0xD6D6A3E8,
0xA1D1937E,0x38D8C2C4,0x4FDFF252,0xD1BB67F1,0xA6BC5767,0x3FB506DD,0x48B2364B,
0xD80D2BDA,0xAF0A1B4C,0x36034AF6,0x41047A60,0xDF60EFC3,0xA867DF55,0x316E8EEF,
0x4669BE79,0xCB61B38C,0xBC66831A,0x256FD2A0,0x5268E236,0xCC0C7795,0xBB0B4703,
0x220216B9,0x5505262F,0xC5BA3BBE,0xB2BD0B28,0x2BB45A92,0x5CB36A04,0xC2D7FFA7,
0xB5D0CF31,0x2CD99E8B,0x5BDEAE1D,0x9B64C2B0,0xEC63F226,0x756AA39C,0x026D930A,
0x9C0906A9,0xEB0E363F,0x72076785,0x05005713,0x95BF4A82,0xE2B87A14,0x7BB12BAE,
0x0CB61B38,0x92D28E9B,0xE5D5BE0D,0x7CDCEFB7,0x0BDBDF21,0x86D3D2D4,0xF1D4E242,
0x68DDB3F8,0x1FDA836E,0x81BE16CD,0xF6B9265B,0x6FB077E1,0x18B74777,0x88085AE6,
0xFF0F6A70,0x66063BCA,0x11010B5C,0x8F659EFF,0xF862AE69,0x616BFFD3,0x166CCF45,
0xA00AE278,0xD70DD2EE,0x4E048354,0x3903B3C2,0xA7672661,0xD06016F7,0x4969474D,
0x3E6E77DB,0xAED16A4A,0xD9D65ADC,0x40DF0B66,0x37D83BF0,0xA9BCAE53,0xDEBB9EC5,
0x47B2CF7F,0x30B5FFE9,0xBDBDF21C,0xCABAC28A,0x53B39330,0x24B4A3A6,0xBAD03605,
0xCDD70693,0x54DE5729,0x23D967BF,0xB3667A2E,0xC4614AB8,0x5D681B02,0x2A6F2B94,
0xB40BBE37,0xC30C8EA1,0x5A05DF1B,0x2D02EF8D };
unsigned long crc32;
unsigned char *byteBuf;
size_t i;
char byte;
/** accumulate crc32 for buffer **/
crc32 = 0;
byteBuf = (unsigned char *) string;
i = 0;
while ((byte = byteBuf[i++])) {
crc32 = (crc32 >> 8) ^ crcTable[ (crc32 ^ byte) & 0xFF ];
}
return( crc32 ^ 0xFFFFFFFF );
}
- (unsigned long)crc32
{
return Crc32_String(0, [self UTF8String]);
}
#end