CODEWITHSUNDEEP
c++arrayscharconstantswarnings
user3001604
user3001604

Reputation: 53

C4838 warning with array initialization of a const char* array

For a project I compile my shaders to binary data and then convert them to a header file that declares the byte code of the shader as a const char array.

However, during compilation I get the following warning:

"conversion from int to const char requires a narrowing conversion".

Now I normally know why this happens, it's because the compiler thinks the values are of type int, while they are in fact declared as a type of char.

const char base_ps[]={
0x44,0x58,0x42,0x43,0x12 ... etc

When hovering over these values IntelliSense also points out these are casted to an int. For instance, for the value at index 0 it lists (int)0x44.

Is there any work around for this? Obviously I can explicity put (char) everywhere before each value, however I'd have to add an extra step into shader generation for this that parses the header file.

I kind of don't want to suppress the warning either, yet I want warnings treated as errors. Any advice on this?

Upvotes: 4

Views: 1709

Answers (2)

AndyG
AndyG

Reputation: 41110

The issue is because you are actually using hex values that are too large to store in a char (which is usually signed and 8 bits long). So the largest positive value is 127, or 0x7F. The values you are providing like you show here include values over 127, hence you get a correct narrowing conversion warning.

Either use an unsigned char instead of char, or use smaller numbers (not larger than 0x7F) like here:

const char deferred_ps[]={
    0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 
    0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
    0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
    0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f,
    0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f,
    0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x5b, 0x5c, 0x5d, 0x5e, 0x5f,
    0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
    0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f
};

Note that if you ignore the narrowing conversion warning, the result is implementation-defined, which is non-portable.

Upvotes: 3

NathanOliver
NathanOliver

Reputation: 180720

You can suppress the warning by using a character literal instead integer literal. With character literals you can use the escape sequence in the form of \xNN to denote a character defined by a hexadecimal value. That would look like

const char foo[] = "\x44\x58\x42\x43";

or

const char foo[] = {'\x44', '\x58', '\x42', '\x43'};

The difference between them is that since the first one is a c string it will add a null terminator to the end. If you do not want that then you need to use the second method.

Upvotes: 3

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