decompile .NET Replace method (v4.6.1)

Question

I want to see how the

public String Replace(String oldValue, String newValue);

method that is inside mscorlib.dll (System.String) works.

I decompiled the mscorlib.dll with dotPeek and inside the method there is a call to ReplaceInternal method which I cannot find it

string s = ReplaceInternal(oldValue, newValue);

I have search for this method even on the open source .NET Core from GIT but no luck.

Please explain where is this method and what is inside?

[`ReplaceInternal`](http://referencesource.microsoft.com/#mscorlib/system/string.cs,35ab9efe11757286) ist `extern`, so most likely it is implemented as "unmanaged", native C++ code. See [P/Invoke](https://en.wikipedia.org/wiki/Platform_Invocation_Services) for details. — Uwe Keim, Sep 09 '16 at 04:49
btw you dont need to decompile, you can see the source @ http://referencesource.microsoft.com/#mscorlib/system/string.cs,69fc1d0aa6df8a90 — Bob, Sep 09 '16 at 04:54

score 7 · Accepted Answer · edited Sep 09 '16 at 05:03

7

The extern C++ code is here.

https://github.com/gbarnett/shared-source-cli-2.0/blob/master/clr/src/vm/comstring.cpp

Line 1578 has

FCIMPL3(Object*, COMString::ReplaceString, StringObject* thisRefUNSAFE, StringObject* oldValueUNSAFE, StringObject* newValueUNSAFE)

edited Sep 09 '16 at 05:03

Cory Nelson

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answered Sep 09 '16 at 05:00

Veener

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1

http://www.codeproject.com/Articles/1014073/Fastest-method-to-trim-all-whitespace-from-Strings?fid=1888684&df=90&mpp=25&prof=False&sort=Position&view=Thread&spc=Relaxed&fr=76 – Veener Sep 09 '16 at 05:04

Christos · Answer 2 · 2016-09-09T05:13:34.787

Having a look here, you will notice this:

// This method contains the same functionality as StringBuilder Replace. 
// The only difference is that
// a new String has to be allocated since Strings are immutable
[System.Security.SecuritySafeCritical]  // auto-generated
[ResourceExposure(ResourceScope.None)]
[MethodImplAttribute(MethodImplOptions.InternalCall)]
private extern String ReplaceInternal(String oldValue, String newValue);

The extern keyword means that this method is implemented externally, in another dll.

That being said, it may be even written in a not managed dll (in C++ quite possibly), that is used by this module. So you can't decompile this code or see it, as you usually do with managed code.

Update

After a little searching I found the corresponding code in the coreclr project:

https://github.com/dotnet/coreclr/blob/master/src/classlibnative/bcltype/stringnative.cpp

Thank you very much, but where is the "another.dll" ? I want to see inside .. or what is his name? — Pacurar Stefan, Sep 09 '16 at 04:55

score 0 · Answer 3 · answered Sep 09 '16 at 05:14

To see how the function works, take a look at the reference source under http://referencesource.microsoft.com/.

Serach for mscorlib, go to System.String, serach for Replace and look: http://referencesource.microsoft.com/#mscorlib/system/string.cs,69fc1d0aa6df8a90,references

decompile .NET Replace method (v4.6.1)

3 Answers3