free char*: invalid next size (fast) [duplicate]

by

Your code is wrong.

You are allocating space for a single pointer (malloc(sizeof(char*))), but no characters. You are overwriting your allocated space with all the strings, causing undefined behavior (in tihs particular case, corrupting malloc()‘s book-keeping data).

You don’t need to allocate space for the pointer (res), it’s a local variable. You must allocate space for all the characters you wish to store at the address held by the pointer.

Since you’re going to be traversing a list to find strings to concatenate, you can’t know the total size upfront. You’re going to have to do two passes over the list: one to sum the strlen() of each string, then allocate that plus space for the separator and terminator, then another pass when you actually do the concatenenation.

More Related Contents:

  1. What REALLY happens when you don’t free after malloc before program termination?
  2. How do free and malloc work in C?
  3. Setting variable to NULL after free
  4. Should I free memory before exit?
  5. C – Accessing data AFTER memory has been free()ed?
  6. malloc implementation?
  7. If free() knows the length of my array, why can’t I ask for it in my own code?
  8. Why do I get different results when I dereference a pointer after freeing it?
  9. C: Correctly freeing memory of a multi-dimensional array
  10. Is freeing allocated memory needed when exiting a program in C
  11. Problem usage memory in C
  12. Why exactly should I not call free() on variables not allocated by malloc()?
  13. How are we able to access the pointer after deallocating the memory?
  14. Code for malloc and free
  15. Why this program is crashing?
  16. How can I get the size of an array from a pointer in C?
  17. What’s the point of malloc(0)?
  18. Overriding ‘malloc’ using the LD_PRELOAD mechanism
  19. Using malloc for allocation of multi-dimensional arrays with different row lengths
  20. Why is malloc not “using up” the memory on my computer?
  21. Writing to pointer out of bounds after malloc() not causing error
  22. Maximum memory which malloc can allocate
  23. Is the compiler allowed to recycle freed pointer variables?
  24. C Warning: Function returns address of local variable
  25. malloc(sizeof(int)) vs malloc(sizeof(int *)) vs (int *)malloc(sizeof(int))
  26. Why do I get a warning every time I use malloc?
  27. An alternative for the deprecated __malloc_hook functionality of glibc
  28. Why does this intentionally incorrect use of strcpy not fail horribly?
  29. Minimizing the amount of malloc() calls improves performance?
  30. new, delete ,malloc & free

Leave a Comment