anyway to delete only part of array?

Question

char myWord[20];

I want to delete last 10 chars of this array, I mean freeing the memory thats being used by last 10 chars. Is there anyway to do this ?

Heres an example function for substring where it might be useful.

str& substring(uint Start, uint Count){
    for(uint x=0; x<Count; x++){
        mString[x] = mString[x+Start];
    }  
    // SOMEHOW FREE MEMORY OF mString FROM [Start+Count] TO [mLength]
    mLength = Count;
    return *this;
}

I don't think you can do this when you've allocated the memory statically (at compile-time) using []. If you use malloc() to allocate your memory dynamically, you can e.g. use realloc() to reduce/enlarge your array. — marnir
– marnir, Commented Jun 5, 2011 at 12:23
It's allocated on the stack so it will all be freed automatically when the containing block ends. Why do you need to "rush" this? — Andrei
– Andrei, Commented Jun 5, 2011 at 12:27
Please understand that C and C++ are very different languages, even if their syntaxes have a lot in common. — dreamlax
– dreamlax, Commented Jun 5, 2011 at 12:43

dreamlax · Accepted Answer · 2011-06-05 12:20:25Z

3

No, not really. You can really only do it if you obtained a pointer to memory from malloc, and then used realloc to change the size, but I'm quite sure that it's not even guaranteed that it will free the unused bytes.

answered Jun 5, 2011 at 12:20

dreamlax

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10 Comments

aeroson Over a year ago

But this will copy the array just with different length ?

dreamlax Over a year ago

Not necessarily, it is possible that the data may end up copied somewhere else, but the end result is that you then have a pointer to memory of 10 bytes, rather than 20 (even if those 10 bytes aren't in the same place that the original 20 were).

Matteo Italia Over a year ago

@aeroson: 10 bytes of memory to keep/free are the last of your problems in a real application. It's probably much more inefficient to call realloc than to keep the buffer 10 bytes larger.

Andrei Over a year ago

@aeronson: realloc is well documented and also reading documentation and understanding it is a valuable skill. go read what realloc does

dreamlax Over a year ago

@aeroson: Then use the .erase() method instead.

|

Matteo Italia · Accepted Answer · 2011-06-05 12:20:50Z

2

With stack-allocated arrays¹, no. You can only use some special character to mark the "logical end" of the array; for strings usually the NUL character (0) is used.

And even with stuff allocated on the heap usually you don't have that much granularity in allocations to free just 10 bytes of a 20-bytes long string.

answered Jun 5, 2011 at 12:20

Matteo Italia

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