Memory free() in C


 
Thread Tools Search this Thread
Top Forums Programming Memory free() in C
# 1  
Old 08-26-2011
Memory free() in C

Hi guys.
I've a question, if we are using a syscall that receives a string allocated dynamicaly to a determined size, or NUL and it will allocate the apropriate size. We should free the memory or the OS will do it for us?
If a function returns a pointer we should free that poiter when we are done with it?

Thanks.
# 2  
Old 08-26-2011
The interface should document memory management responsibilities.
# 3  
Old 08-26-2011
1, Only memory allocated explicitly or implicitly by malloc() should be free() manually (explicitly or use wrapper of free).

2, If you don't free them, OS will recycle them when the process terminates. But this causes memory leak.

3, depend on they type of the memory. If it is static memory, you need not and you can't. If it is allocated by malloc() you need.

4, you should explicitly free() memory if you called strdup() because it is a wrapper of malloc(), and it doesn't give a wrapper of free().
This User Gave Thanks to vistastar For This Post:
# 4  
Old 08-26-2011
free(3) is not a system call.

from gnu.org GLIBC manual
Quote:
Occasionally, free can actually return memory to the operating system and make the process smaller. Usually, all it can do is allow a later call to malloc to reuse the space. In the meantime, the space remains in your program as part of a free-list used internally by malloc.
This User Gave Thanks to frank_rizzo For This Post:
# 5  
Old 08-27-2011
Thank you so much for your reply. I am working with your approach but I'm getting errors when I call free(), I allocated a portion of memory with malloc() and when I call free() I get a error , if I comment out the free() instruction the program runs without this error.
Does you or anyone knows the cause?

Code:
*** glibc detected *** ./prog: free(): invalid pointer: 0x000000000160fd2b ***
======= Backtrace: =========
/lib/libc.so.6(+0x7366a)[0x7f5aaa03a66a]
/lib/libc.so.6(cfree+0x6c)[0x7f5aaa03e54c]
./prog[0x40286f]
./prog[0x4028e2]
./prog[0x40136f]
/lib/libc.so.6(__libc_start_main+0xed)[0x7f5aa9fe817d]
./prog[0x400e29]
======= Memory map: ========
00400000-00404000 r-xp 00000000 08:02 671794                             /home/pharaoh/Development/c_lang/pa_ficha6/exer_2/prog
00603000-00604000 rw-p 00003000 08:02 671794                             /home/pharaoh/Development/c_lang/pa_ficha6/exer_2/prog
0160f000-01630000 rw-p 00000000 00:00 0                                  [heap]
7f5aa4000000-7f5aa4021000 rw-p 00000000 00:00 0 
7f5aa4021000-7f5aa8000000 ---p 00000000 00:00 0 
7f5aa9db1000-7f5aa9dc6000 r-xp 00000000 08:02 2565373                    /usr/lib/libgcc_s.so.1
7f5aa9dc6000-7f5aa9fc6000 ---p 00015000 08:02 2565373                    /usr/lib/libgcc_s.so.1
7f5aa9fc6000-7f5aa9fc7000 rw-p 00015000 08:02 2565373                    /usr/lib/libgcc_s.so.1
7f5aa9fc7000-7f5aaa11e000 r-xp 00000000 08:02 16446                      /lib/libc-2.14.so
7f5aaa11e000-7f5aaa31e000 ---p 00157000 08:02 16446                      /lib/libc-2.14.so
7f5aaa31e000-7f5aaa322000 r--p 00157000 08:02 16446                      /lib/libc-2.14.so
7f5aaa322000-7f5aaa323000 rw-p 0015b000 08:02 16446                      /lib/libc-2.14.so
7f5aaa323000-7f5aaa328000 rw-p 00000000 00:00 0 
7f5aaa328000-7f5aaa33f000 r-xp 00000000 08:02 16394                      /lib/libpthread-2.14.so
7f5aaa33f000-7f5aaa53f000 ---p 00017000 08:02 16394                      /lib/libpthread-2.14.so
7f5aaa53f000-7f5aaa540000 r--p 00017000 08:02 16394                      /lib/libpthread-2.14.so
7f5aaa540000-7f5aaa541000 rw-p 00018000 08:02 16394                      /lib/libpthread-2.14.so
7f5aaa541000-7f5aaa545000 rw-p 00000000 00:00 0 
7f5aaa545000-7f5aaa564000 r-xp 00000000 08:02 16467                      /lib/ld-2.14.so
7f5aaa73d000-7f5aaa740000 rw-p 00000000 00:00 0 
7f5aaa760000-7f5aaa763000 rw-p 00000000 00:00 0 
7f5aaa763000-7f5aaa764000 r--p 0001e000 08:02 16467                      /lib/ld-2.14.so
7f5aaa764000-7f5aaa765000 rw-p 0001f000 08:02 16467                      /lib/ld-2.14.so
7f5aaa765000-7f5aaa766000 rw-p 00000000 00:00 0 
7fff3cd3a000-7fff3cd5b000 rw-p 00000000 00:00 0                          [stack]
7fff3cdff000-7fff3ce00000 r-xp 00000000 00:00 0                          [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]
Aborted

# 6  
Old 08-27-2011
can you post the code around the free? Looks like your giving it an invalid address to free.
# 7  
Old 08-28-2011
You must free() the original pointer returned by malloc() without any arithmetic option to it.
Login or Register to Ask a Question

Previous Thread | Next Thread

10 More Discussions You Might Find Interesting

1. Solaris

How the free memory threshold?

If I understand your question correctly, you are asking for an explanation of Solaris memory manager. You'd better ask Oracle that question because you are talking about Solaris kernel internals. The operating system kernel has no reason to kick a process's memory set out of real memory until... (4 Replies)
Discussion started by: hicksd8
4 Replies

2. Solaris

Is there a way to free up memory manually ?

Hi, I am wondering if there is a way to free up memory in Solaris manually ? the way we can do it in Linux for example : echo `/bin/date` "************* Memory Info Before *************" free -m sync echo 1 > /proc/sys/vm/drop_caches echo 2 > /proc/sys/vm/drop_caches echo 3 >... (13 Replies)
Discussion started by: terrykhatri531
13 Replies

3. AIX

How to find AIX Free Memory?

All, AIX: 6.1 64 bits How to find out Free memory available on AIX 6.1 64 bits When I used : svmon -G size inuse free pin virtual mmode memory 1048576 612109 191151 215969 549824 Ded-E pg space 4325376 ... (1 Reply)
Discussion started by: a1_win
1 Replies

4. UNIX for Advanced & Expert Users

Out of Memory error when free memory size is large

I was running a program and it stopped and showed "Out of Memory!". at that time, the RAM used by this process is around 4G and the free memory size of the machine is around 30G. Does anybody know what maybe the reason? this program is written with Perl. the OS of the machine is Solaris U8. And I... (1 Reply)
Discussion started by: lilili07
1 Replies

5. Red Hat

how to find out free memory?

hi, I have done the below, but am confused as to how much memory is "free" please help thanks $ free total used free shared buffers cached Mem: 132033488 48827536 83205952 0 1007696 45404632 -/+ buffers/cache: 2415208 ... (7 Replies)
Discussion started by: JamesByars
7 Replies

6. Solaris

how to get the more memory free space (see memory free column)

Hi all, Could please let me know how to get the more memory free space (not added the RAM) in local zone. -bash-3.00# vmstat 2 5 kthr memory page disk faults cpu r b w swap free re mf pi po fr de sr s0 s1 s1 s1 in sy cs us sy... (3 Replies)
Discussion started by: murthy76
3 Replies

7. Solaris

How to find Total and Free Physical Memory and Logical Memory in SOLARIS 9

Hi, Im working on Solaris 9 on SPARC-32 bit running on an Ultra-80, and I have to find out the following:- 1. Total Physical Memory in the system(total RAM). 2. Available Physical Memory(i.e. RAM Usage) 3. Total (Logical) Memory in the system 4. Available (Logical) Memory. I know... (4 Replies)
Discussion started by: 0ktalmagik
4 Replies

8. AIX

Free Memory in aix

Hi, I want to know how to find out free physical memory in aix, (11 Replies)
Discussion started by: manoj.solaris
11 Replies

9. AIX

Free Memory

Hi, how to find free memory in aix? for installing oracle,I have used svmon but not getting proper output (1 Reply)
Discussion started by: manoj.solaris
1 Replies

10. Programming

How to free the memory?

For example if i have the piece of code as follows: CountryName = (char *)malloc((strlen(CountryName)+1)*sizeof(char)); memset(CountryName, 0, strlen(CountryName)+1); CountryName = SOME VALUE Now how do i free the memory after use of this code???? :confused: (3 Replies)
Discussion started by: jazz
3 Replies
Login or Register to Ask a Question