Free() and release placement issue

Question

-(NSString *)trimTaskOutput:(NSString *)taskString{
NSString * string;
string = [taskString retain];
[taskString release];
NSCharacterSet * numericSet = [NSCharacterSet characterSetWithCharactersInString:@"9876543210"];
NSRange startingPointOfNumericSet = [string rangeOfCharacterFromSet:numericSet];
int scanValue = ([string length] - startingPointOfNumericSet.location);
NSRange allNumericValues = NSMakeRange(startingPointOfNumericSet.location,scanValue );
void * buf = malloc([string length] * sizeof(char));
[string getBytes:buf maxLength:scanValue usedLength:nil encoding:NSASCIIStringEncoding options:nil range:allNumericValues remainingRange:nil];
NSString * final = [[NSString alloc]initWithBytes:buf length:sizeof(buf) encoding:NSASCIIStringEncoding];
free(buf);
[string release];
[final autorelease];
return final;
When placing "free(buf)" under "[string release]" my program crashes, my question is, why? I'm assuming that it is because either "[string getBytes:....]" is referencing that pointer still or the init method for the "final" string is still referencing it. If one of those two assumptions is the reason, why does it matter if I free before I release an object?
If neither of those is the reason can anyone shed some light on why that method crashes when free is after one of the release calls at the bottom.

Answer 1

Eric Lundquist wrote:
I switched it from void * to char * , I'm trying to get only the numbers at the end of a string returned from an NSTask
One pointer is the same as the next.
1) sizeof(any pointer type) will always return 4 on a 32-bit machine or 8 on a 64-bit machine.
2) You are using very, very low-level "Bytes" methods with very, very high-level NSStrings. There are no C strings here. There are no null terminators. Confused? Then don't use those methods.
Your original code, even without the memory errors, did not return valid results. Here is the correct code. I'm too old and stubborn to read other people's code, so I always reformat it so I don't have to work so hard:
#import <Foundation/Foundation.h>
NSString * func(NSString * taskString);
int main (int argc, const char * argv[])
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
// insert code here...
NSLog(@"Hello, World!");
NSString * taskString = @"hello1234";
NSString * result = func(taskString);
NSLog(@"Result is: %@", result);
[pool drain];
return 0;
NSString * func(NSString * taskString)
NSString * string;
NSString * final;
if (taskString != nil)
string = [taskString retain];
[taskString release];
else
return nil;
NSCharacterSet * numericSet =
[NSCharacterSet characterSetWithCharactersInString:@"9876543210"];
NSRange startingPointOfNumericSet =
[string rangeOfCharacterFromSet: numericSet];
int scanValue =
([string length] - startingPointOfNumericSet.location);
NSRange allNumericValues =
NSMakeRange(startingPointOfNumericSet.location, scanValue);
char * buf = malloc(scanValue * sizeof(char));
if([string
getBytes: buf
maxLength: scanValue
usedLength: NULL
encoding: NSASCIIStringEncoding
options: NSStringEncodingConversionAllowLossy
range: allNumericValues
remainingRange: 0])
final =
[[NSString alloc]
initWithBytes: buf
length: [string length]
encoding: NSASCIIStringEncoding];
if(buf != NULL)
free(buf);
else
return nil;
if(string != nil)
[string release];
return final;