Why use c strings in c++?

Question

Is there any good reason to use C-strings in C++ nowadays? My textbook uses them in examples at some points, and I really feel like it would be easier just to use a std::string

Answer 1

Memory control. I recently had to handle strings (actually blobs from a database) about 200-300 MB in size, in a massively multithreaded application. It was a situation where just-one-more copy of the string might have burst the 32bit address space. I had to know exactly how many copies of the string existed. Although I'm an STL evangelist, I used char * then because it gave me the guarantee that no extra memory or even extra copy was allocated. I knew exactly how much space it would need.

Apart from that, standard STL string processing misses out on some great C functions for string processing/parsing. Thankfully, std::string has the c_str() method for const access to the internal buffer. To use printf() you still have to use char * though (what a crazy idea of the C++ team to not include (s)printf-like functionality, one of the most useful functions EVER in C. I hope boost::format will soon be included in the STL.

Answer 2

The only reasons I've had to use them is when interfacing with 3rd party libraries that use C style strings. There might also be esoteric situations where you would use C style strings for performance reasons, but more often than not, using methods on C++ strings is probably faster due to inlining and specialization, etc.

You can use the c_str() method in many cases when working with those sort of APIs, but you should be aware that the char * returned is const, and you should not modify the string via that pointer. In those sort of situations, you can still use a vector<char> instead, and at least get the benefit of easier memory management.

Answer 3

Textbooks feature old-school C strings because many basic functions still expect them as arguments, or return them. Additionally, it gives some insight into the underlying structure of the string in memory.

Answer 4

If the C++ code is "deep" (close to the kernel, heavily dependent on C libraries, etc.) you may want to use C strings explicitly to avoid lots of conversions in to and out of std::string. Of, if you're interfacing with other language domains (Python, Ruby, etc.) you might do so for the same reason. Otherwise, use std::string.

Answer 5

For applications such as most embedded platforms where you do not have the luxury of a heap to store the strings being manipulated, and where deterministic preallocation of string buffers is required.

Answer 6

It depends on the libraries you're using. For example, when working with the MFC, it's often easier to use CString when working with various parts of the Windows API. It also seems to perform better than std::string in Win32 applications.

However, std::string is part of the C++ standard, so if you want better portability, go with std::string.