how to avoid (potential) memory leak

I have a for loop where at the beginning an NSObject "value" is declared and then a switch statement within "value" is actually created. "value" then can be an NSNumber, an NSDate, an NSData, an NSString or nil. This is the code:

for (int i = 0; i < self.columnCount; i++) {
  NSObject *value;
  switch (mysql_fields[i].type) {
    case ...
      ...
    case MYSQL_TYPE_LONG:
      value = [[NSNumber alloc] initWithInt:atoi(row[i])];
      /* [value autorelease]; */  // 2)
      break;
    case MYSQL_TYPE_DECIMAL:
      NSString *decimal = [[NSString alloc] initWithCString:(char *)row[i] encoding:NSUTF8StringEncoding];
      value = [[NSDecimalNumber alloc] initWithString:decimal];
      /* [value autorelease]; */  // 2)
      [decimal release];
      break;
    case ...
      ...
  } // end of switch
} end of for
Field *field = [[[Field alloc] initWithRecord:record] autorelease];
/* [value autorelease]; */  // 3)
[field setValue:value forKey:@"value"];
/* [value release]; */  // 4)

Now I don't know how to release "value". This is what I tried and the corresponding Xcode 4 "Analyzer" messages:

  • no release -> "potential leak"
  • [value autorelease] after alloc/init within each case statement -> "object sent autorelease too many times"
  • [value autorelease] directly before the last use -> "object sent autorelease too many times"
  • [value release] after the last use -> "Incorrect decrement of the reference count of an object not owned by the caller at this point"

  • 仅在分配对象时添加autorelease,删除其余部分:

    value = [[[NSNumber alloc] initWithInt:atoi(row[i])] autorelease];
    // ....
    value = [[[NSDecimalNumber alloc] initWithString:decimal] autorelease];
    

    你在for循环中声明了value ,所以你必须在开关后面释放它,但是在for循环中。

    for (int i = 0; i < self.columnCount; i++)
    {
        NSObject *value;
        switch (mysql_fields[i].type)
        {
            case ...
                ...
            case MYSQL_TYPE_LONG:
                value = [[NSNumber alloc] initWithInt:atoi(row[i])];
                break;
            case MYSQL_TYPE_DECIMAL:
                NSString *decimal = [[NSString alloc] initWithCString:(char *)row[i] encoding:NSUTF8StringEncoding];
                value = [[NSDecimalNumber alloc] initWithString:decimal];
                [decimal release];
                break;
            case ...
                ...
        }
        Field *field = [[[Field alloc] initWithRecord:record] autorelease];
        [field setValue:value forKey:@"value"];
        [value release];
    }
    
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