Those are called #include guards. Once the header is included, it checks if a unique value (in this case HEADERFILE_H) is defined. Then if it’s not defined, it defines it and continues to the rest of the page. When the code is included again, the first ifndef fails, resulting in a blank file. That prevents … Read more
If you mean a C-style array, then you can do something like: int a[7]; std::cout << “Length of array = ” << (sizeof(a)/sizeof(*a)) << std::endl; This doesn’t work on pointers (i.e. it won’t work for either of the following): int *p = new int[7]; std::cout << “Length of array = ” << (sizeof(p)/sizeof(*p)) << std::endl; … Read more
Put yourself in the compiler’s position: when you forward declare a type, all the compiler knows is that this type exists; it knows nothing about its size, members, or methods. This is why it’s called an incomplete type. Therefore, you cannot use the type to declare a member, or a base class, since the compiler … Read more
For Linux and I believe Mac OS X, if you’re using gcc, or any compiler that uses glibc, you can use the backtrace() functions in execinfo.h to print a stacktrace and exit gracefully when you get a segmentation fault. Documentation can be found in the libc manual. Here’s an example program that installs a SIGSEGV … Read more
Use std::string::find as follows: if (s1.find(s2) != std::string::npos) { std::cout << “found!” << ‘\n’; } Note: “found!” will be printed if s2 is a substring of s1, both s1 and s2 are of type std::string.
Answer recommended by Intel
If your compiler supports C++11, you can simply do: std::vector<int> v = {1, 2, 3, 4}; This is available in GCC as of version 4.4. Unfortunately, VC++ 2010 seems to be lagging behind in this respect. Alternatively, the Boost.Assign library uses non-macro magic to allow the following: #include <boost/assign/list_of.hpp> … std::vector<int> v = boost::assign::list_of(1)(2)(3)(4); Or: … Read more
In C++11 there are some nice new convert functions from std::string to a number type. So instead of atoi( str.c_str() ) you can use std::stoi( str ) where str is your number as std::string. There are version for all flavours of numbers: long stol(string), float stof(string), double stod(string),… see http://en.cppreference.com/w/cpp/string/basic_string/stol
There are a couple of possibilities. One I like uses a stringstream as a go-between: std::ifstream t(“file.txt”); std::stringstream buffer; buffer << t.rdbuf(); Now the contents of “file.txt” are available in a string as buffer.str(). Another possibility (though I certainly don’t like it as well) is much more like your original: std::ifstream t(“file.txt”); t.seekg(0, std::ios::end); size_t … Read more
typename and class are interchangeable in the basic case of specifying a template: template<class T> class Foo { }; and template<typename T> class Foo { }; are equivalent. Having said that, there are specific cases where there is a difference between typename and class. The first one is in the case of dependent types. typename … Read more