std::malloc
Defined in header <cstdlib> | ||
void* malloc(std::size_t size ); | ||
Allocates size bytes of uninitialized storage.
If allocation succeeds, returns a pointer to the lowest (first) byte in the allocated memory block that is suitably aligned for any scalar type (at least as strictly as std::max_align_t) (implicitly creating objects in the destination area).
If size is zero, the behavior is implementation defined (null pointer may be returned, or some non-null pointer may be returned that may not be used to access storage, but has to be passed to std::free).
The following functions are required to be thread-safe:
Calls to these functions that allocate or deallocate a particular unit of storage occur in a single total order, and each such deallocation call happens-before the next allocation (if any) in this order. | (since C++11) |
Contents |
[edit]Parameters
| size | - | number of bytes to allocate |
[edit]Return value
On success, returns the pointer to the beginning of newly allocated memory. To avoid a memory leak, the returned pointer must be deallocated with std::free() or std::realloc().
On failure, returns a null pointer.
[edit]Notes
This function does not call constructors or initialize memory in any way. There are no ready-to-use smart pointers that could guarantee that the matching deallocation function is called. The preferred method of memory allocation in C++ is using RAII-ready functions std::make_unique, std::make_shared, container constructors, etc, and, in low-level library code, new-expression.
For loading a large file, file mapping via OS-specific functions, e.g. mmap on POSIX or CreateFileMapping(A/W) along with MapViewOfFile on Windows, is preferable to allocating a buffer for file reading.
[edit]Example
#include <cstdlib> #include <iostream> #include <memory>#include <string> int main(){constexprstd::size_t size =4;if(auto ptr =reinterpret_cast<std::string*>(std::malloc(size * sizeof(std::string)))){try{for(std::size_t i =0; i < size;++i)std::construct_at(ptr + i, 5, 'a'+ i);for(std::size_t i =0; i < size;++i)std::cout<<"ptr["<< i <<"] == "<< ptr[i]<<'\n';std::destroy_n(ptr, size);}catch(...){}std::free(ptr);}}
Output:
p[0] == aaaaa p[1] == bbbbb p[2] == ccccc p[3] == ddddd
[edit]See also
| allocation functions (function) | |
(deprecated in C++17)(removed in C++20) | obtains uninitialized storage (function template) |
C documentation for malloc | |
