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Defined in header <cstdlib> | ||
void* malloc(std::size_t size); | ||
Allocatessize 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 asstd::max_align_t) (implicitly creating objects in the destination area).
Ifsize 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 tostd::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 callhappens-before the next allocation (if any) in this order. | (since C++11) |
Contents |
| size | - | number of bytes to allocate |
On success, returns the pointer to the beginning of newly allocated memory. To avoid a memory leak, the returned pointer must be deallocated withstd::free() orstd::realloc().
On failure, returns a null pointer.
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 functionsstd::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 orCreateFileMapping(A/W) along withMapViewOfFile on Windows, is preferable to allocating a buffer for file reading.
#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] == aaaaap[1] == bbbbbp[2] == cccccp[3] == ddddd
| allocation functions (function)[edit] | |
(deprecated in C++17)(removed in C++20) | obtains uninitialized storage (function template)[edit] |
C documentation formalloc | |
