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std::string provides const char* c_str ( ) const which:
Get C string equivalent
Generates a null-terminated sequence of characters (c-string) with the same content as the string object and returns it as a pointer to an array of characters.
A terminating null character is automatically appended.
The returned array points to an internal location with the required storage space for this sequence of characters plus its terminating null-character, but the values in this array should not be modified in the program and are only granted to remain unchanged until the next call to a non-constant member function of the string object.
Why don't they just define operator const char*() const {return c_str();}?
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The c_str() and strcpy() function in C++C++ c_str() function along with C++ String strcpy() function can be used to convert a string to char array easily. The c_str() method represents the sequence of characters in an array of string followed by a null character ('\0').
Use std::string when you need to store a value. Use const char * when you want maximum flexibility, as almost everything can be easily converted to or from one.
std::string is almost always preferred. Even for speed, it uses small array on the stack before dynamically allocating more for larger strings. However, char* pointers are still needed in many situations for writing strings/data into a raw buffer (e.g. network I/O), which can't be done with std::string.
The main reason for using const char* is because it is compatible and linkable with C. Many APIs and other libraries have C interfaces (you use the API via a collection of C-like functions).
From the C++ Programming Language 20.3.7 (emphasis mine):
Conversion to a C-style string could have been provided by an operator const char*() rather than c_str(). This would have provided the convenience of an implicit conversion at the cost of surprises in cases in which such a conversion was unexpected.
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