C++ – Difference Between string.c_str() and &string[0]

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What are the differences between string.c_str() and &string[0]?

Regarding performance my guess is that &string[0] is a little faster than string.c_str() as it doesn't require a function call.

Regarding safety and stability common sense tells me that string.c_str() should have some checks implemented, but I don't know, that's why I'm asking.

Best Answer

In C++98 there is no guarantee that the internal array is null terminated; in other words string.data()[string.size()] results in undefined behavior. The implementation will then reallocate the array with the null termination when c_str() is called but can leave the null terminator off when it isn't.

This also means that &string[0] is not guaranteed to be null terminated (it is essentially a detour to data())

In C++11 the null termination guarantee is specified so string.data()==string.c_str() is always valid.

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