malloc(sizeof(int)) means you are allocating space off the heap to store an int. You are reserving as many bytes as an int requires. This returns a value you should cast to int *. (A pointer to an int.) As some have noted, typical practice in C is to let implicit casting take care of this. malloc(sizeof(int*)) means you are allocating space off the heap … Read more
You can’t cast anything to a structure type. What I presume you meant to write is: But please don’t cast the return value of malloc() in a C program. Will work just fine and won’t hide #include bugs from you.
This error occurs because some other part of your code has corrupted the heap. We can’t tell you what that error is without seeing the rest of the code. The fact that FINE 7 is not printed tells you that realloc is failing. And that failure must be because buffer is invalid due to a heap corruption earlier in the execution. … Read more
As I can understand from your assignment statement in while loop I think you need array of strings instead: Note: By doing = in while loop as below: you are just assigning address of string (its not deep copy), but because you are also writing “only address of strings” so I think this is what you wants. … Read more
I am writing my own functions for malloc and free in C for an assignment. I need to take advantage of the C sbrk() wrapper function. From what I understand sbrk() increments the program’s data space by the number of bytes passed as an argument and points to the location of the program break. If … Read more
Yes, it’s a matter of style, because you’d expect sizeof(char) to always be one. On the other hand, it’s very much an idiom to use sizeof(foo) when doing a malloc, and most importantly it makes the code self documenting. Also better for maintenance, perhaps. If you were switching from char to wchar, you’d switch to … Read more
Before I read your code. Valgrind reporting invalid free error is not because of leaked memory, but you try to free invalid memory (or free same memory more than once). Compiling your code with the compilter flag -g (gdb debug), will enable more debug information, making the backtraces from valgrind much better. A quick guess:
char is a character and sizeof(char) is defined to be 1. (N1570 6.5.3.4 The sizeof and _Alignof operators, paragraph 4) char* is a pointer to a character and sizeof(char*) depends on the environment. It is typically 4 in 32-bit environment and 8 in 64-bit environment. In typical environment where sizeof(char*) > sizeof(char), malloc(sizeof(char*)*len + 1) will (at least try to) allocate more memory than malloc(sizeof(char)*len + 1) if len is small … Read more
In read_response, you are probably overwriting the end of the buffer pointed to by buf. The problem is that buf is a pointer, so sizeof(buf) will return the size of a pointer (probably 4 or 8 depending on your CPU). You are using sizeof as if buf were an array, which is not really the same thing as a pointer in C although … Read more
malloc() returns a void* pointer to a block of memory stored in the heap. Allocating with malloc() does not initialize any string, only space waiting to be occupied.To add a null-terminating character, you either have to do this yourself, or use a function like scanf(), which adds this character for you. Having said this, you … Read more