lnt-arithmetic-overflow.md

title	description	ms.date	f1_keywords	helpviewer_keywords	monikerRange
lnt-arithmetic-overflow	Reference for Visual Studio C++ IntelliSense Linter check lnt-arithmetic-overflow.	09/29/2021	lnt-arithmetic-overflow	lnt-arithmetic-overflow	>=msvc-160

lnt-arithmetic-overflow

An arithmetic expression may overflow before being converted to a wider type.

In C and C++, arithmetic operations are evaluated using the widest type of the operands, not the width of the type assigned the result. When a result is converted to a wider type, it indicates the developer expects the operation may overflow the narrower types of the operands.

The lnt-arithmetic-overflow check is controlled by the Arithmetic Overflow setting in the C/C++ Code Style options. For information on how to change this setting, see Configure the linter.

Examples

#include <cstdint>

void overflow(int a, int b) {
    int64_t mul = a * b;      // Flagged: 32-bit operation may overflow.
    int64_t shift = a << 34;  // Flagged: Shift would overflow.

    int64_t mul2 = mul + b;   // OK: 'mul' is 64-bit so the addition expression is
                              // evaluated using 64-bit operations.
}

How to fix this issue

The fix the linter suggests is to explicitly widen one of the operands. Then the entire expression is evaluated at the wider result type, as shown in this example:

void overflow(int a, int b) {
    int64_t mul = static_cast<int64_t>(a) * b;
    int64_t shift = static_cast<int64_t>(a) << 34;
}

See also

IntelliSense code linter for C++ overview