Error: `alloc-dealloc-mismatch`

2025-05-30

Address Sanitizer Error: Mismatch between allocation and deallocation APIs

Enables runtime detection of mismatched memory operations that may lead to undefined behavior, such as:

malloc must be paired with free, not delete or delete[].
new must be paired with delete, not free or delete[].
new[] must be paired with delete[], not delete or free.

In Windows, alloc-dealloc-mismatch error detection is off by default. To enable it, set the environment variable set ASAN_OPTIONS=alloc_dealloc_mismatch=1 before running your program.

Example

// example1.cpp
// Demonstrate alloc-dealloc-mismatch error
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char* argv[])
{
    if (argc != 2) return -1;

    switch (atoi(argv[1]))
    {
        case 1:
            delete[](new int[10]);
            break;
        case 2:
            delete (new int[10]);      // Boom!
            break;
        default:
            printf("arguments: 1: no error 2: runtime error\n");
            return -1;
    }
    return 0;
}

In a Visual Studio 2019 version 16.9 or later developer command prompt, run the following commands to see an exampe of alloc_dealloc_mismatch:

cl example1.cpp /fsanitize=address /Zi
set ASAN_OPTIONS=alloc_dealloc_mismatch=1
devenv /debugexe example1.exe 2

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Error: alloc-dealloc-mismatch

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Error: `alloc-dealloc-mismatch`