Finding Size of data

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Consider the below fragment of code :

C++

char * str = nullptr;
str = new char[sz]

Here 'sz' is to be sought by the program during runtime.

My question is : How to find the size of str ? Neither sizeof() operator nor strlen() function work.

Posted 20-May-13 8:02am

compuknow

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Ron Beyer · Answer 1 · 2013-05-20T08:18:00

Solution 1

The size of the str will equal sz. strlen won't work because it loops until it finds the null string terminator '\0'. Since you've got a new char array, all the characters are probably '\0'.

Maybe you aren't explaining it very well, is "sz" being passed into a function, or are you trying to find out what value to assign to sz? sz should be an integer value greater than 0.

Posted 20-May-13 8:18am

Ron Beyer

Comments

CPallini 20-May-13 16:52pm

5.

Andreas Gieriet 20-May-13 17:28pm

The allocated memory will most likely be random data and not all '\0'. C++ base types have no implicit initial value (unlike other languages like Java and C#). So, if the str variable comes from outside, there is no way to determine its allocated capacity. See also my solution #2 for alternative data structures that allow to properly handle capacity and actual stored data length.
Cheers
Andi

compuknow 20-May-13 22:33pm

I am trying to get the size of a file as sz.
Will it work if create a clone of strlen with a difference only that it checks for the eof character?

Andreas Gieriet · Answer 2 · 2013-05-20T11:20:00

Solution 2

I regard using char* str = new char[sz]; as deprecated/anachronistic.
If you do string handling, try using std::string str = ...; or if you work on raw memory try using std::vector<char> mem;. Both are smart enough to handle the dynamic memory in a decent way, i.e. you do not have to care about new/malloc/calloc/strdup/... and delete/delete[]/free/...
See http://www.cplusplus.com/reference/string/string/[^] and http://www.cplusplus.com/reference/vector/vector/[^].

Cheers
Andi

Posted 20-May-13 11:20am

Andreas Gieriet

Updated 20-May-13 11:29am

v2

Comments

compuknow 20-May-13 22:40pm

Are vectors useful to store entire file content of a binary file? May be using a read command.

Andreas Gieriet 21-May-13 4:26am

See the first solution in How to copy a file into a vector? (C++).
Cheers
Andi
PS: Vectors are very useful in managing binary dynamic data arrays.