How do I free memory in C

Question

I m writing code which has a lot of 1  amp  2 dimensional arrays  I got  error  can t allocate region  and I think its because too much memory is allocated  I use  malloc  and  free  functions  but I m not sure I m using them correclyt  Maybe you know where I could see good examples on memory management in C   so   I just trying to get one algorithm work and for now this code is just function after function      memory allocation for 1D arrays buffer   malloc num items sizeof double       memory allocation for 2D arrays double   cross norm  double   malloc 150   sizeof double      for i 0  i lt 150 i                  cross norm i   double  malloc num items sizeof double                 code Window N  window buffer   STFTforBMP buffer N f  window buffer   getMagnitude buffer f  N  magnitude   calculateEnergy flux magnitude  f   calculateExpectedEnergy expected flux  candidate beat period  downbeat location  f   calculateCrossCorrelation cross  flux  expected values  f   findLargestCrossCorrelation  amp cross max  cross  f   normalizeCrossCorrelation cross norm   amp cross max  cross  f                         How should I use the free function

User · Answer

You actually can t manually  free  memory in C  in the sense that the memory is released from the process back to the OS     when you call malloc    the underlying libc-runtime will request from the OS a memory region   On Linux  this may be done though a relatively  heavy  call like mmap     Once this memory region is mapped to your program  there is a linked-list setup called the  free store  that manages this allocated memory region   When you call malloc    it quickly looks though the free-store for a free block of memory at the size requested   It then adjusts the linked list to reflect that there has been a chunk of memory taken out of the originally allocated memory pool   When you call free   the memory block is placed back in the free-store as a linked-list node that indicates its an available chunk of memory   If you request more memory than what is located in the free-store  the libc-runtime will again request more memory from the OS up to the limit of the OS s ability to allocate memory for running processes   When you free memory though  it s not returned back to the OS     it s typically recycled back into the free-store where it can be used again by another call to malloc     Thus  if you make a lot of calls to malloc   and free   with varying memory size requests  it could  in theory  cause a condition called  memory fragmentation   where there is enough space in the free-store to allocate your requested memory block  but not enough contiguous space for the size of the block you ve requested   Thus the call to malloc   fails  and you re effectively  out-of-memory  even though there may be plenty of memory available as a total amount of bytes in the free-store

User · Answer

You have to free   the allocated memory in exact reverse order of how it was allocated using malloc          Note that You should free the memory only after you are done with your usage of the allocated pointers        memory allocation for 1D arrays           buffer   malloc num items sizeof double      memory deallocation for 1D arrays           free buffer     memory allocation for 2D arrays              double   cross norm  double   malloc 150   sizeof double          for i 0  i lt 150 i                  cross norm i   double  malloc num items sizeof double            memory deallocation for 2D arrays           for i 0  i lt 150 i                  free cross norm i               free cross norm

[c] How do I free memory in C?

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