A variable is assigned a constant in a Boolean context.

An assignment expression that takes a constant always evaluates to the value of the constant. A comparison operation, such as == or !=, was probably intended instead.

::: moniker range=">=msvc-170"

In Visual Studio 2022, The lnt-assignment-equality check is controlled by the Accidental Assignment setting in the C/C++ Code Style options. For information on how to change this setting, see Configure the linter.

::: moniker-end ::: moniker range="msvc-160"

In Visual Studio 2019, the lnt-assignment-equality check is controlled by the Assignation Instead of Equality setting in the C/C++ Code Style options. For information on how to change this setting, see Configure the linter.

::: moniker-end

int read();

void accidental_assignment(int i)
{
    if (i = 2) {}       // Flagged: 'i' is being assigned to a constant.

    if (i = read()) {}  // OK: 'i' is being assigned the result of a function call.

    while (i = 0) {}    // Flagged.
}

The fix the linter suggests is to change the assignment operator to an equality operator.

void accidental_assignment(int i)
{
    if (i == 2) {}

    while (i != 0) {}
}

This check only flags assignment from a constant or constant expression.

void known_issues(bool b) {
    if (b = true) {}  // Not flagged because there is no implicit conversion to bool.
}

IntelliSense code linter for C++ overview