Why do you prefer char* instead of string, in C++?

Question

I'm a C programmer trying to write c++ code. I heard string in C++ was better than char* in terms of security, performance, etc, however sometimes it seems that char* is a better choice. Someone suggested that programmers should not use char* in C++ because we could do all things that char* could do with string, and it's more secure and faster.

Did you ever used char* in C++? What are the specific conditions?

Answer 1

The only time I've recently used a C-style char string in a C++ program was on a project that needed to make use of two C libraries that (of course) used C strings exclusively. Converting back and forth between the two string types made the code really convoluted.

I also had to do some manipulation on the strings that's actually kind of awkward to do with std::string, but I wouldn't have considered that a good reason to use C strings in the absence of the above constraint.

Answer 2

Ok, the question changed a lot since I first answered.

Native char arrays are a nightmare of memory management and buffer overruns compared to std::string. I always prefer to use std::string.

That said, char array may be a better choice in some circumstances due to performance constraints (although std::string may actually be faster in some cases -- measure first!) or prohibition of dynamic memory usage in an embedded environment, etc.

Answer 3

In general, std::string is a cleaner, safer way to go because it removes the burden of memory management from the programmer. The main reason it can be faster than char *'s, is that std::string stores the length of the string. So, you don't have to do the work of iterating through the entire character array looking for the terminating NULL character each time you want to do a copy, append, etc.

That being said, you will still find a lot of c++ programs that use a mix of std::string and char *, or have even written their own string classes from scratch. In older compilers, std::string was a memory hog and not necessarily as fast as it could be. This has gotten better over time, but some high-performance applications (e.g., games and servers) can still benefit from hand-tuned string manipulations and memory-management.

I would recommend starting out with std::string, or possibly creating a wrapper for it with more utility functions (e.g., starts_with(), split(), format(), etc.). If you find when benchmarking your code that string manipulation is a bottleneck, or uses too much memory, you can then decide if you want to accept the extra risks and testing that a custom string library demands.

TIP: One way of getting around the memory issues and still use std::string is to use an embedded database such as SQLite. This is particularly useful when generating and manipulating extremely large lists of strings, and performance is better than what you might expect.

Answer 4

Compare and contrast the following C and C++ examples:

strlen(infinitelengthstring)

versus

string.length()

Answer 5

String may actually be better in terms of performance. And innumerable other reasons - security, memory management, convenient string functions, make std::string an infinitely better choice.

Edit: To see why string might be more efficient, read Herb Sutter's books - he discusses a way to internally implement string to use Lazy Initialization combined with Referencing.

Answer 6

Use std::string for its incredible convenience - automatic memory handling and methods / operators. With some string manipulations, most implementations will have optimizations in place (such as delayed evaluation of several subsequent manipulations - saves memory copying).

If you need to rely on the specific char layout in memory for other optimizations, try std::vector<char> instead. If you have a non-empty vector vec, you can get a char* pointer using &vec[0] (the vector has to be nonempty).