Error free invalid next size fast

Question

What is this strange error I m getting  I m compiling C   using g   on Ubuntu 10 10  It pops up randomly when I run the executable  maybe 2 times in 8 hours  with 10 compiles an hour   However  if I make clean and recompile it goes away most of the time       glibc detected       emailQueue app  free    invalid next size  fast   0x0000000001c40270             Backtrace             lib libc so 6  0x774b6  0x7f490d95e4b6   lib libc so 6 cfree 0x73  0x7f490d964c83    emailQueue app 0x401f47   lib libc so 6   libc start main 0xfe  0x7f490d905d8e    emailQueue app 0x401cc9          Memory map           00400000-0040d000 r-xp 00000000 08 01 1311132                             home server Projects email emailQueue app 0060d000-0060e000 r--p 0000d000 08 01 1311132                             home server Projects email emailQueue app 0060e000-0060f000 rw-p 0000e000 08 01 1311132                             home server Projects email emailQueue app 01c40000-01c82000 rw-p 00000000 00 00 0                                   heap  7f4908000000-7f4908021000 rw-p 00000000 00 00 0  7f4908021000-7f490c000000 ---p 00000000 00 00 0  7f490ce52000-7f490ce5e000 r-xp 00000000 08 01 1051251                     lib libnss files-2 12 1 so 7f490ce5e000-7f490d05d000 ---p 0000c000 08 01 1051251                     lib libnss files-2 12 1 so 7f490d05d000-7f490d05e000 r--p 0000b000 08 01 1051251                     lib libnss files-2 12 1 so 7f490d05e000-7f490d05f000 rw-p 0000c000 08 01 1051251                     lib libnss files-2 12 1 so 7f490d05f000-7f490d075000 r-xp 00000000 08 01 1048770                     lib libz so 1 2 3 4 7f490d075000-7f490d275000 ---p 00016000 08 01 1048770                     lib libz so 1 2 3 4 7f490d275000-7f490d276000 r--p 00016000 08 01 1048770                     lib libz so 1 2 3 4 7f490d276000-7f490d277000 rw-p 00017000 08 01 1048770                     lib libz so 1 2 3 4 7f490d277000-7f490d28e000 r-xp 00000000 08 01 1051248                     lib libnsl-2 12 1 so 7f490d28e000-7f490d48d000 ---p 00017000 08 01 1051248                     lib libnsl-2 12 1 so 7f490d48d000-7f490d48e000 r--p 00016000 08 01 1051248                     lib libnsl-2 12 1 so 7f490d48e000-7f490d48f000 rw-p 00017000 08 01 1051248                     lib libnsl-2 12 1 so 7f490d48f000-7f490d491000 rw-p 00000000 00 00 0  7f490d491000-7f490d49a000 r-xp 00000000 08 01 1051244                     lib libcrypt-2 12 1 so 7f490d49a000-7f490d69a000 ---p 00009000 08 01 1051244                     lib libcrypt-2 12 1 so 7f490d69a000-7f490d69b000 r--p 00009000 08 01 1051244                     lib libcrypt-2 12 1 so 7f490d69b000-7f490d69c000 rw-p 0000a000 08 01 1051244                     lib libcrypt-2 12 1 so 7f490d69c000-7f490d6ca000 rw-p 00000000 00 00 0  7f490d6ca000-7f490d6e2000 r-xp 00000000 08 01 1051256                     lib libpthread-2 12 1 so 7f490d6e2000-7f490d8e1000 ---p 00018000 08 01 1051256                     lib libpthread-2 12 1 so 7f490d8e1000-7f490d8e2000 r--p 00017000 08 01 1051256                     lib libpthread-2 12 1 so 7f490d8e2000-7f490d8e3000 rw-p 00018000 08 01 1051256                     lib libpthread-2 12 1 so 7f490d8e3000-7f490d8e7000 rw-p 00000000 00 00 0  7f490d8e7000-7f490da61000 r-xp 00000000 08 01 1048743                     lib libc-2 12 1 so 7f490da61000-7f490dc60000 ---p 0017a000 08 01 1048743                     lib libc-2 12 1 so 7f490dc60000-7f490dc64000 r--p 00179000 08 01 1048743                     lib libc-2 12 1 so 7f490dc64000-7f490dc65000 rw-p 0017d000 08 01 1048743                     lib libc-2 12 1 so 7f490dc65000-7f490dc6a000 rw-p 00000000 00 00 0  7f490dc6a000-7f490dc7f000 r-xp 00000000 08 01 1048655                     lib libgcc s so 1 7f490dc7f000-7f490de7e000 ---p 00015000 08 01 1048655                     lib libgcc s so 1 7f490de7e000-7f490de7f000 r--p 00014000 08 01 1048655                     lib libgcc s so 1 7f490de7f000-7f490de80000 rw-p 00015000 08 01 1048655                     lib libgcc s so 1 7f490de80000-7f490df02000 r-xp 00000000 08 01 1051246                     lib libm-2 12 1 so 7f490df02000-7f490e101000 ---p 00082000 08 01 1051246                     lib libm-2 12 1 so 7f490e101000-7f490e102000 r--p 00081000 08 01 1051246                     lib libm-2 12 1 so 7f490e102000-7f490e103000 rw-p 00082000 08 01 1051246                     lib libm-2 12 1 so 7f490e103000-7f490e1eb000 r-xp 00000000 08 01 4853329                     usr lib libstdc   so 6 0 14 7f490e1eb000-7f490e3ea000 ---p 000e8000 08 01 4853329                     usr lib libstdc   so 6 0 14 7f490e3ea000-7f490e3f2000 r--p 000e7000 08 01 4853329                     usr lib libstdc   so 6 0 14 7f490e3f2000-7f490e3f4000 rw-p 000ef000 08 01 4853329                     usr lib libstdc   so 6 0 14 7f490e3f4000-7f490e409000 rw-p 00000000 00 00 0  7f490e409000-7f490e5c7000 r-xp 00000000 08 01 4851315                     usr lib libmysqlclient so 16 0 0 7f490e5c7000-7f490e7c7000 ---p 001be000 08 01 4851315                     usr lib libmysqlclient so 16 0 0 7f490e7c7000-7f490e7cc000 r--p 001be000 08 01 4851315                     usr lib libmysqlclient so 16 0 0 7f490e7cc000-7f490e816000 rw-p 001c3000 08 01 4851315                     usr lib libmysqlclient so 16 0 0 7f490e816000-7f490e817000 rw-p 00000000 00 00 0  7f490e817000-7f490e837000 r-xp 00000000 08 01 1048597                     lib ld-2 12 1 so 7f490ea15000-7f490ea1c000 rw-p 00000000 00 00 0  7f490ea33000-7f490ea37000 rw-p 00000000 00 00 0  7f490ea37000-7f490ea38000 r--p 00020000 08 01 1048597                     lib ld-2 12 1 so 7f490ea38000-7f490ea39000 rw-p 00021000 08 01 1048597                     lib ld-2 12 1 so 7f490ea39000-7f490ea3a000 rw-p 00000000 00 00 0  7fffb85b9000-7fffb85da000 rw-p 00000000 00 00 0                           stack  7fffb85ff000-7fffb8600000 r-xp 00000000 00 00 0                           vdso  ffffffffff600000-ffffffffff601000 r-xp 00000000 00 00 0                   vsyscall  Aborted

User · Answer

I encountered the same problem  even though I did not make any dynamic memory allocation in my program  but I was accessing a vector s index without allocating memory for it   So  if the same case  better allocate some memory using resize   and then access vector elements

User · Answer

I encountered a similar error  It was a noob mistake done in a hurry  Integer array without declaring size int a   then trying to access it  C   compiler should ve caught such an error easily if it were in main  However since this particular int array was declared inside an object  it was being created at the same time as my object  many objects were being created  and the compiler was throwing a free    invalid next size normal  error  I thought of 2 explanations for this  please enlighten me if anyone knows more   1   This resulted in some random memory being assigned to it but since this wasn t accessible it was freeing up all the other heap memory just trying to find this int  2   The memory required by it was practically infinite for a program and to assign this it was freeing up all other memory   A simple       int  a      class foo       foo           for i 0 i lt n i               a new int i            Solved the problem  But it did take a lot of time trying to debug this because the compiler could not  really  find the error

User · Answer

If you are trying to allocate space for an array of pointers  such as  char   my array of strings      or some array of pointers such as int   or even void     then you will need to consider word size  8 bytes in a 64-bit system  4 bytes in a 32-bit system  when allocating space for n pointers   The size of a pointer is the same of your word size   So while you may wish to allocate space for n pointers  you are actually going to need n times 8 or 4  for 64-bit or 32-bit systems  respectively   To avoid overflowing your allocated memory for n elements of 8 bytes   my array of strings    char    malloc  n   8        for 64-bit systems my array of strings    char    malloc  n   4        for 32-bit systems   This will return a block of n pointers  each consisting of 8 bytes  or 4 bytes if you re using a 32-bit system   I have noticed that Linux will allow you to use all n pointers when you haven t compensated for word size  but when you try to free that memory it realizes its mistake and it gives out that rather nasty error   And it is a bad one  when you overflow allocated memory  many security issues lie in wait

User · Answer

I encountered such a situation where code was circumventing STL s api and writing to the array unsafely when someone resizes it  Adding the assert here caught it    void Logo  add const QVector3D  amp v  const QVector3D  amp n     GLfloat  p   m data data     m count    p     v x      p     v y      p     v z      p     n x      p     n y      p     n z     m count    6   Q ASSERT  m count  lt   m data size

User · Answer

We need the code  but that usually pops up when you try to free   memory from a pointer that is not allocated  This often happens when you re double-freeing

User · Answer

It means that you have a memory error   You may be trying to free a pointer that wasn t allocated by malloc  or delete an object that wasn t created by new  or you may be trying to free delete such an object more than once   You may be overflowing a buffer or otherwise writing to memory to which you shouldn t be writing  causing heap corruption   Any number of programming errors can cause this problem   You need to use a debugger  get a backtrace  and see what your program is doing when the error occurs   If that fails and you determine you have corrupted the heap at some previous point in time  you may be in for some painful debugging  it may not be too painful if the project is small enough that you can tackle it piece by piece

[c++] Error: free(): invalid next size (fast):

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