Why does C++ allow an integer to be assigned to a string?

Question

I encountered an interesting situation today in a program where I inadvertantly assigned an unsigned integer to a std::string. The VisualStudio C++ compiler did not give an

Answer 1

The std::string class has the following assignment operator defined:

string& operator=( char ch );

This operator is invoked by implicit conversion of unsigned int to char.

In your third case, you are using an explicit constructor to instantiate a std::string, none of the available constructors can accept an unsigned int, or use implicit conversion from unsigned int:

string();
string( const string& s );
string( size_type length, const char& ch );
string( const char* str );
string( const char* str, size_type length );
string( const string& str, size_type index, size_type length );
string( input_iterator start, input_iterator end );

Answer 2

It is definitely operator=(char ch) call - my debugger stepped into that. And my MS VS 2005 compiles following without error.

std::string my_string("");
unsigned int my_number = 1234;
my_string = my_number;
my_string.operator=(my_number);

Answer 3

Because string is assignable from char, and int is implicitly convertible to char.

Answer 4

I can explain the first and third situations:

my_string = 1234;

This works because string has overridden operator=(char). You are actually assigning a character (with data overflow) into the string. I don't know why the second case results in a compile error. I tried the code with GCC and it does compile.

std::string my_string(1234);

will not work, because there is no string constructor that takes a char or int argument.