Question

My problem is the following:

• a const char* is provided to the function in which I would like to perform the operation I am going to describe
• what is provided is a filename (full absolute path included) of indeterminate length
• I would like to locate the occurrence of the substring output and replace it with input
• the output of these operations must be another const char* (too much code to change to replace it with a std::string)

What I was thinking to do is the following

string name(filename); //filename is the "const char*" provided by the caller of the function
string portion("output");
name.replace(name.find(insert),insert.length(),"input");
const char* newfilename = (char*)name.c_str();

Now, my questions:

• would do this work?
• is there a better way to obtain what I need?

Thanks to anyone that will help.

Federico

Answer 1

This will work, but you don’t need the cast on name.c_str() (in fact, it’s wrong: c_str() returns a const char *).

But the pointer you get from name.c_str() is invalidated as soon as you modify name, or when name goes out of scope. So don’t try returning newfilename from a function, for instance.

If you need it to persist, you have no option but to dynamically allocate memory. Standard practice would be to use a smart pointer to automatically manage deallocation.const char *, you have no option but to manage this yourself. So you could do:

char *newfilename = new char[name.length() + 1];
strcpy(newfilename, name.c_str());
return newfilename;
...

delete [] newfilename;

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_{* Well, standard practice would be to use a std::string! It only gets tricky if you need to interface with a legacy C API.}