Question

I have a program that reads a huge text file (line by line) and does some string operations with each line before writing the line into a database.

The program needed more and more memory so I figured that I might need to release the strings that I use. But it did not help. So I have put together the following code to test out what actually happens. With some trial and error I found out that when I do the drain on the autorelease pool it works.

I would like to know what I do. So I ask:

• Why is the release not releasing memory?
• Is there a better way to do this?

Here is my test program

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[]) {

NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

int cnt = 0;

while (cnt < 1000000000) {
    NSMutableString *teststr = [[NSMutableString alloc] init];

    teststr = [NSString stringWithString:@"Dummy string just for the demo"];

    cnt++;
    if (cnt % 1000000 == 0) {
        printf("cnt=%i\n",cnt);
    }

    [teststr release];


//      [pool drain];                      // It works when I do this 
//      [[NSAutoreleasePool alloc] init];  // and this

}

[pool drain];
return 0;
}

EDIT: Based on the answers so far I have looked on my original program and changed the test program:

//teststr = [NSString stringWithString:@"Dummy string just for the demo"];

[teststr appendString:@"Dummy string just for the demo"];

Does this also create a new string? Because still I have the memory problem. My routine works in way that I append the string with something but maybe start with an empty string at the beginning.

Answer 1

NSMutableString *teststr = [[NSMutableString alloc] init];

This allocates a mutable string….

teststr = [NSString stringWithString:@"Dummy string just for the demo"];

and then this overrides the teststr variable with an autoreleased string. The allocated mutable string is now inaccessible, but still having a retain count of +1, so it will be leaked.

[teststr release];

This will only release the autoreleased string, causing double-free error in the future.

---

If you want a manually-managed mutable string, you should use

NSMutableString* teststr = [[NSMutableString alloc] initWithString:@"Dummy string just for the demo"];
...
[teststr release];

and don’t assign to teststr directly, before it is released or the ownership is transferred.