动态分配的字符串

Question

I have defined a struct that stores the length and content of a string.

struct sir {
    int length;
    char* string;
};

I am trying to dynamically alocate memory space for this string using:

s->string = malloc(sizeof(char) * (s->length));

But I keep getting this error:

error C2440: '=' : cannot convert from 'void *' to 'char *' 

Can you please guide in finishing this function?

PS: I would really like to know how write values from keyboard in this newly created string? Tnx in advance!

Answer 1

malloc() will return void * , which needs to be converted to char * explicitly in C++ (though not needed in C ).

Try

s->string = (char *) malloc(sizeof(char) * (s->length));

---

Edit: As you're using C++ , as @chris commented, you should consider to use std::string instead. No manual memory management is needed. If you must do it yourself, use new instead of malloc .

Answer 2

You are compiling the program as a C++ program. The return type of function malloc is void * However a pointer to void may not be implicitly converted to a pointer to other type in C++ and the error message says about this clear enough.

So write

s->string = ( char * )malloc(sizeof(char) * (s->length));. 

However the coorect way is to use operator new instead of malloc in C++

s->string = new char[s->length];. 

Again if it is a C++ program then instead of the structure it would be better to use a class with explicitly defined constructors, destructor and the copy bassignment operator.

Or compile your program as a C program if you indeed want to deal with a C program.