compiler-warning-level-3-c4018.md

title	description	ms.date	f1_keywords	helpviewer_keywords
Compiler Warning (level 3) C4018	Microsoft C/C++ compiler warning C4018, its causes and resolution.	10/16/2020	C4018	C4018

Compiler Warning (level 3) C4018

'token' : signed/unsigned mismatch

Using the token operator to compare signed and unsigned numbers required the compiler to convert the signed value to unsigned.

Remarks

One way to fix this warning is if you cast one of the two types when you compare signed and unsigned types.

Example

This sample generates C4018 and shows how to fix it:

// C4018.cpp
// compile with: cl /EHsc /W4 C4018.cpp
int main() {
    unsigned int uc = 0;
    int c = 0;
    unsigned int c2 = c; // implicit conversion

    if (uc < c)           // C4018
        uc = 0;

    if (uc < unsigned(c)) // OK
        uc = 0;

    if (uc < c2)          // Also OK
       uc = 0;
}

See also

Compiler Warning (Level 4) C4388
Compiler Warning (Level 4) C4389