c - How to get memory block length after malloc? -

-

I thought I could assign the length of the allocated memory block to .length function in Java though, now I know that when allocates the block to malloc () , it allocates extra bytes to keep the block-shaped integer it is located at the beginning of the integer block; This address was actually transferred to the number of the collar, which is exactly past the value of this length. The problem is, I can not access that address to retrieve the block length 

  #include & lt; Stdlib.h & gt; # Include & lt; Stdio.h & gt; Int main (zero) {four * str; Str = (four *) maulok (size (four) * 1000); Int * length; Length = str-4; / * Because on 32 bit system, one int 4 bytes long * / printf ("str length:% d \ n", * length); Free (STR); } Edit: Lastly I did the problem, this is giving 0 on my system as a length instead of size because my Ubuntu is 64 bit. I have changed str-4 to str-8, and it works now.  
 If I change the size to 2000, then it produces a length up to 2017. However, when I change to 3000, it gives 300 9. I am using GCC.   
 
 
 What you are doing is certainly wrong, though it is almost certain that allocated blocks Just before the word is related to the shape, it may contain information in some extra flags or unused bits. Depending on the implementation, this data may also be in  high  bits, causing you to completely read the wrong length. Apart from this, it is also possible that small allocations (such as 1 to 32 bytes) are packaged in special small-block pages, in which there are no headers, in this case the word before the allotted block is just another block There is no meaning in relation to the part and size of the blocks are examining.  
 Just stop this misguided and dangerous pursuit if you need to know the size of the block from the  malloc , then you are doing something wrong.

Comments

Post a Comment

Popular posts from this blog

qt - switch/case statement in C++ with a QString type -

-
I want to use switch-case in my program but the compiler generates an error. How can I use the switch statement with QString ? The compiler gives me this error: The expression of the switch type 'QString' is invalid My code is as follows : boolStopWord (the word QString) {bool flag = false; Switch (word) {case "the": flag = true; break ; "On" case: flag = true; break ; Case "in": flag = true; break ; Case "your": flag = true; break ; Case "near": flag = true; break ; Case "all": flag = true; break ; Case "this": flag = true; break ; } Return flag; } How do I use the switch statement with a Caststring ? You can not use the switch statement in C ++ language with integral or enum types. You can formally enter the square type of object in the switch statement, but this means that the compiler will look for a user-defined conversion to convert it to an integral or enum type.
Read more

python - sqlite3.OperationalError: near "REFERENCES": syntax error - foreign key creating -

-
I'm trying to create a predefined key after checking the manual and I wrote it: Db.execute ("create table" Table 2 (id, integer primary key, somedata integer) "db.execute" (table creation table 2 does not exist (name text, maintain reference (id) ") and found this: sqlite 3. Operation error: near" references ": syntax error Your second ligne is wrong db.execute ("create table if table does not exist 2 (name text, my_id integer, foreign key (my_id) reference Maintenance (ID)) ") as explained
Read more

Python's equivalent for Ruby's define_method? -

-
What is a Python equivalent for Ruby's define_method , which is the dynamic generation of class methods will allow? (As can be seen in Wikipedia) Functions are first-class objects in Python and assign them The properties of a class or an example can be a way of doing the same thing as a Wikipedia example: colors = {"black": "000", "red": "F00", "green": "0f0", "yellow": "ff0", "blue": "00f", "magenta": "fff", "cyan": "0ff", "white": " FFF "} Class MyStream (ARR): Pass for Name, Code in colors.iteritems (): def _in_colour ( W code = code): return '& lt; Span style = "color:% s" & gt;% s & lt; / Span & gt; ' % (Code, self) setter (histrive, "in_" + name, _in_ color)
Read more