Passing char * parameter to C# function

Question

C++ win32dll1.dll:

extern "C" __declspec(dllexport) int getSerialNumber(char* outs)
{
    char s[2];
    s[0]='0';
    s[1]='1';

    for(int i=0; i < 2; ++i){
        outs[i] = s[i];
    }
    return 1;
}

C#:

[DllImport("win32dll1.dll")]
public unsafe static extern int getSerialNumber(char* ss);

Not able to pass s in the function

char[] s = new char[2];
getSerialNumber(s);

Shouldn't this work? Why or why not?

possible duplicates stackoverflow.com/questions/683013/… stackoverflow.com/questions/2179270/… stackoverflow.com/questions/4455234/… — Rotem
– Rotem, Commented Dec 2, 2012 at 10:09

Timwi · Accepted Answer · 2012-12-02 10:14:43Z

3

You should probably use StringBuilder in the declaration:

[DllImport("win32dll1.dll")]
public unsafe static extern int getSerialNumber(StringBuilder s);

The CLR will automatically translate that to C++ char*, call the function, and then convert the result back and store it in the StringBuider.

Call it with something like this:

var sb = new StringBuilder(2);
getSerialNumber(sb);

The number specifies the initial capacity in characters. In this example, it’s only 2 characters; if the C++ code writes more than that, your app will crash.

edited Dec 2, 2012 at 10:14

answered Dec 2, 2012 at 10:09

Timwi

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3 Comments

Konrad Rudolph Over a year ago

I don’ think OP wants a string. Looking at the example data provided in the question, I think byte[] would be more appropriate.

Security Hound Over a year ago

@KonradRudolph - They can just convert the String into a byte[] in that case. Who knows what the author want their question was vague.

Timwi Over a year ago

The example in the question clearly puts characters into an array in a method called getSerialNumber, which clearly means to retrieve a text string.

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