C function only works with string literal

I'm trying to use a C function created by someone else.

here's it's declaration:

Code:

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static void MDString(char *);

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The code works just fine if I call the function like this:

Code:

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MDString ("someString");

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but it won't work if I call it with a c string from the console:

Code:

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  char *input;
  cout<< endl << "Enter a string to be hashed: ";
  cin>>input;
  MDString(input);

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I had been working on this problem earlier today and I got it to work :) ... but then I tried to clean up the code a few hours later and it no longer works :(

It compiles but crashes as soon as I call the function

I can't remember What I did, only that I only changed the code you see above. What are String Literals terminated with? Are they terminated at all? I think the answer might have something to do with that.

Does >> leave the \n at the end of the input? (I'm asking because I don't know.) If it does, that may lead to a different result.

Edit: Or, to miss the obvious, do you ever allocate space for this string? You have a pointer, but you don't own the memory it points to (at least in the snippet you posted).

to call in such way

Code:

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MDString ("someString");

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you should declare it as

Code:

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static void MDString(const char *);

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in this case, to avoid messing with allocations you can write your snipplet as

Code:

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  std::string input;
  cout<< endl << "Enter a string to be hashed: ";
  cin>>input;
  MDString(input.c_str());

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But I do not understand 1 thing - if your functon does not modify the original string and does not return value, what it DOES do?

Quote:

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Originally Posted by vart

to call in such way

Code:

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  std::string input;
  cout<< endl << "Enter a string to be hashed: ";
  cin>>input;
  MDString(input.c_str());

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That's exactly what I did and with one little modification:

Code:

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MDString((char*)input.c_str());

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It works

Quote:

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Originally Posted by vart

But I do not understand 1 thing - if your functon does not modify the original string and does not return value, what it DOES do?

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It's an implementation of the MD4 algorithm. I took it from the 1992 memo and Spent today getting rid of there compiler specific macros so that I could actually use it.

It prints out the hashed string within it's self which is why it's not apparent. I'm gonna change that to get it to do what I want.

Thanks vart

Code:

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MDString((char*)input.c_str());

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You tell the function that the passed string is modifiable. But it is not. So your asking for trouble. Better change the function prototype to accept const char*.

Quote:

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You tell the function that the passed string is modifiable. But it is not. So your asking for trouble. Better change the function prototype to accept const char*.

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Will do. The value doesn't get modified in the function but just in case I mess some part of it up I'll do that. C doesn't have a const keyword does it?


Thanks for your help

> C doesn't have a const keyword does it?
Why wouldn't it?

Quote:

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Originally Posted by A10

C doesn't have a const keyword does it?

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Only if you use some stone-age compiler