double free or corruption prev error in c program

Question

I get the following error when running a c program       glibc detected       a out  double free or corruption   prev   0x080b8008       I believe this is due to free   being called at the end of the program  but I can t figure out where the malloc d memory is being freed prior to this  Here is the code    include  lt stdio h gt   include  lt stdlib h gt    malloc  include  lt math h gt     sine   define TIME 255  define HARM 32  int main  void        double sineRads      double sine      int tcount   0      int hcount   0         allocate some heap memory for the large array of waveform data        double  ptr   malloc sizeof double      TIME       if  NULL    ptr            printf  ERROR  couldn t allocate waveform memory  n          else             evaluate and add harmonic amplitudes for each time step            for tcount   0  tcount  lt   TIME  tcount                 for hcount   0  hcount  lt   HARM  hcount                     sineRads     double tcount    double TIME     2 M PI     angular frequency                 sineRads     hcount   1     scale frequency by harmonic number                 sine   sin sineRads                      ptr tcount     sine    add to other results for this time step                                 free ptr           ptr   NULL                 return 0      This is compiled with   gcc -Wall -g -lm test c   Valgrind   valgrind --leak-check yes   a out   gives         3028   Memcheck  a memory error detector   3028   Copyright  C  2002-2009  and GNU GPL d  by Julian Seward et al    3028   Using Valgrind-3 6 0 SVN-Debian and LibVEX  rerun with -h for copyright info   3028   Command    a out   3028      3028   Invalid read of size 8   3028      at 0x8048580  main  test c 25    3028    Address 0x41ca420 is 1 016 bytes inside a block of size 1 020 alloc d   3028      at 0x4024F20  malloc  vg replace malloc c 236    3028      by 0x80484F8  main  test c 15    3028      3028   Invalid write of size 8   3028      at 0x8048586  main  test c 25    3028    Address 0x41ca420 is 1 016 bytes inside a block of size 1 020 alloc d   3028      at 0x4024F20  malloc  vg replace malloc c 236    3028      by 0x80484F8  main  test c 15    3028      3028      3028   HEAP SUMMARY    3028       in use at exit  0 bytes in 0 blocks   3028     total heap usage  1 allocs  1 frees  1 020 bytes allocated   3028      3028   All heap blocks were freed -- no leaks are possible   3028      3028   For counts of detected and suppressed errors  rerun with  -v   3028   ERROR SUMMARY  8514 errors from 2 contexts  suppressed  14 from 7    I don t have much experience with languages which don t manage their own memory automatically  hence this exercise in c to learn a bit  but am stuck  Any help would be appreciated   The code is supposed to be part of an additive audio synthesiser  In that respect it does work and gives the correct output stored in ptr   Thanks

User · Accepted Answer

double  ptr   malloc sizeof double      TIME             for tcount   0  tcount  lt   TIME  tcount                                    You re overstepping the array  Either change  lt   to  lt  or alloc SIZE   1 elements Your malloc is wrong  you ll want sizeof double  instead of sizeof double    As ouah comments  although not directly linked to your corruption problem  you re using   ptr tcount  without initializing it      Just as a style note  you might want to use ptr tcount  instead of   ptr   tcount  You don t really need to malloc   free since you already know SIZE

User · Answer

I didn t check all the code but my guess is that the error is in the malloc call  You have to replace    double  ptr   malloc sizeof double     TIME     for    double  ptr   malloc sizeof double    TIME     since you want to allocate size for a double  not the size of a pointer to a double

User · Answer

Change this line  double  ptr   malloc sizeof double      TIME     to  double  ptr   malloc sizeof double    TIME

User · Answer

1 - Your malloc   is wrong   2 - You are overstepping the bounds of the allocated memory  3 - You should initialize your allocated memory   Here is the program with all the changes needed  I compiled and ran    no errors or warnings    include  lt stdio h gt   include  lt stdlib h gt    malloc  include  lt math h gt     sine  include  lt string h gt    define TIME 255  define HARM 32  int main  void        double sineRads      double sine      int tcount   0      int hcount   0         allocate some heap memory for the large array of waveform data        double  ptr   malloc sizeof double    TIME          memset  ptr  0x00  sizeof double    TIME    may not always set double to 0     for  tcount   0  tcount  lt  TIME  tcount                    ptr tcount    0              tcount   0      if  NULL    ptr            printf  ERROR  couldn t allocate waveform memory  n          else             evaluate and add harmonic amplitudes for each time step            for tcount   0  tcount  lt  TIME  tcount                 for hcount   0  hcount  lt   HARM  hcount                     sineRads     double tcount    double TIME     2 M PI     angular frequency                 sineRads     hcount   1     scale frequency by harmonic number                 sine   sin sineRads                    ptr tcount     sine    add to other results for this time step                                 free ptr           ptr   NULL                 return 0

[c] double free or corruption (!prev) error in c program

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