Frequently asked questions about the Standard C++ library

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Standard C++ Libraries Frequently Asked Questions

Q1: What does the Standard C++ library contain?

A1: The Standard C++ library provides an extensible framework and contains components for language support, diagnostics, general utilities, strings, locales, standard template library (containers, iterators, algorithms, and numerics), and input/output.

The Standard C++ library can be divided into the following categories:

1. Standard Template Library (STL) components provide a C++ program with access to a subset of the most widely-used algorithms and data structures. STL headers can be grouped into three major organizing concepts:
   • Containers: template classes that support common ways to organize data, such as <vector>, <list>, <deque>, <stack>, <queue>, <set>, and <map>.
   • Algorithms: template functions for performing common operations on sequences of objects, such as <functional>, <algorithm>, and <numeric>.
   • Iterators: the glue that pastes algorithms and containers together, such as <utility>, <iterator>, and <memory>.
2. Input/Output includes components for forward declarations of iostreams (<iosfwd>), predefined iostreams objects (<iostream>), base iostreams classes (<ios>), stream buffering (<streambuf>), stream formatting and manipulators (<iosmanip>, <istream>, <ostream>), string streams (<sstream>), and file streams (<fstream>).
3. Other Standard C++ headers include:
   • Language Support: components for common type definitions used throughout the library (<cstddef>), characteristics of the predefined types (<limits>, <cfloat>, <climits>), functions supporting start and termination of a C++ program (<cstdlib>), support for dynamic memory management (<new>), support for dynamic type identification (<typeinfo>), support for exception processing (<exception>), and other runtime support (<cstdarg>, <ctime>, <csetlmp>, <csignal>).
   • Diagnostics: components for reporting several kinds of exceptional conditions (<stdexcept>),documenting program assertions (<cassert>), and a global variable for error number codes (<cerrno>).
   • Strings: components for string classes (<string>) and null-terminated sequence utilities (<cctype>, <cwctype>, <cwchar>).
   • Localization: components that C++ programs may use to encapsulate cultural differences. The locale facility includes internationalization support for character classification and string collation, numeric, monetary, and date/time formatting and parsing, and message retrieval (<locale>, <clocale>).

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Q2: What is the difference between C-Runtime library and Standard C++ library? What libraries will the Runtime library compiler options such as /ML, /MT, /MD, /MLd, /MTd, and /MDd include?

A2: Visual C++ 5.0 and later include the following libraries in addition to the Microsoft Foundation Classes (MFC) libraries:

• Basic C-Runtime library.
• Standard C++ library.
• Old iostream library.

      |--------------------------------|---------------------------|
      | Library types and              |    Basic C Runtime        |
      | related compiler switches      |        library            |
      |--------------------------------|---------------------------|
      | Single-threaded (ML)           |    LIBC.lib               |
      | Multithreaded (MT)             |    LIBCMT.lib             |
      | Multithreaded DLL version (MD) |    MSVCRT.lib (import     |
      |                                |    library for            |
      |                                |    MSVCRT.dll)            |
      | Debug single-threaded (MLd)    |    LIBCD.lib              |
      | Debug multithreaded (MTd)      |    LIBCMTD.lib            |
      | Debug multithreaded DLL (MDd)  |    MSVCRTD.lib (import    |
      |                                |    library for            |
      |                                |    MSVCRTD.dll)           |
      |------------------------------------------------------------|

      |--------------------------------|---------------------------|
      | Library types and              |      Standard C++         |
      | related compiler switches      |        library            |
      |--------------------------------|---------------------------|
      | Single-threaded (ML)           |    LIBCP.lib              |
      | Multithreaded (MT)             |    LIBCPMT.lib            |
      | Multithreaded DLL version (MD) |    MSVCPRT.lib*(Also uses |
      |                                |             MSVCRT.dll)   |
      | Debug single-threaded (MLd)    |    LIBCPD.lib             |
      | Debug multithreaded (MTd)      |    LIBCPMTD.lib           |
      | Debug multithreaded DLL (MDd)  |    MSVCPRTD.lib* (Also    |
      |                                |        uses MSVCRTD.dll)  |
      |------------------------------------------------------------|
				

* NOTE: MSVCPRT.lib and MSVCPRTD.lib are static libraries and do not have any dynamic link libraries (DLLs) directly related to them. These libraries are also dependent on MSVCRT.dll and MSVCRTD.dll, respectively. If you have any applications that use MSVCPRT.lib or MSVCPRTD.lib and you use the "Ignore Default Library" (/NOD or NODEFAULTLIB) option, be sure to link MSVCPRT.lib (or MSVCPRTD.lib) and MSVCRT.lib (or MSVCRTD.lib) with your application. Otherwise, you will get linker errors (LNK2001: unresolved externals in MSVCPRT.lib or MSVCPRTD.lib) when linking your application.)

      |--------------------------------|---------------------------|
      | Library types and              |      Old iostream         |
      | related compiler switches      |        library            |
      |--------------------------------|---------------------------|
      | Single-threaded (ML)           |    LIBCI.lib              |
      | Multithreaded (MT)             |    LIBCIMT.lib            |
      | Multithreaded DLL version (MD) |    MSVCIRT.lib (import    |
      |                                |    library for            |
      |                                |    MSVCIRT.dll)           |
      | Debug single-threaded (MLd)    |    LIBCID.lib             |
      | Debug multithreaded (MTd)      |    LIBCIMTD.lib           |
      | Debug multithreaded DLL (MDd)  |    MSVCIRTD.lib (import   |
      |                                |    library for            |
      |                                |    MSVCIRTD.dll)          |
      |------------------------------------------------------------|
				

In Visual C++ 5.0 and later, there are certain default libraries that your program will link with. When you build a release version of your project, one of the basic C-Runtime Libraries (LIBC.lib, LIBCMT.lib, or MSVCRT.lib) is linked by default, depending on the compiler option you choose (single-threaded <ML[d]>, multithreaded <MT[d]>, or DLL<ML[d]>). Depending on the headers you use in your code, a library from the Standard C++ library or one from the old iostream library may also be linked.

For example, if you specify the /ML (single-thread version) compiler option and include <iostream>, a Standard C++ library header, the libraries LIBC.lib and LIBCP.lib are linked with your application by default. If you specify the /ML (single-thread version) compiler option and include <iostream.h>, an old iostream header, the libraries LIBC.lib and LIBCI.lib are linked with your application by default.

Headers determine whether the Standard C++ Libraries and old iostream Libraries will be linked. Compiler options (/ML[d], /MT[d], /MD[d]) determine which version of the libraries (single-threaded, multithreaded, or DLL) is to be linked by default.

NOTE: It may seem that headers without the ".h" extension are Standard C++ headers and ones with the ".h" extension are C-Runtime headers or old iostream headers. This is not true. As explained below, the files <useoldio.h> and <use_ansi.h> determine the libraries with which your application will link.

Actually, there are two header files, <useoldio.h> and <use_ansi.h>, that contain #pragmas. The #pragmas force either the old iostream library or the Standard C++ library to be linked in by default.

The header file <useoldio.h> contains #pragma statements that force the old iostream library to be linked in. All old iostream headers include <useoldio.h>: If you include any old iostream header in your application, the old iostream library will be linked by default.

      |-------------------------|
      |  Old iostream headers   |
      |-------------------------|
      |                         |
      | FSTREAM.H  | IOMANIP.H  |
      | IOS.H      | IOSTREAM.H |
      | ISTREAM.H  | OSTREAM.H  |
      | STDIOSTR.H | STREAMB.H  |
      | STRSTREA.H |            |
      |-------------------------|
				

The header file <use_ansi.h> contains #pragma statements that force the Standard C++ library to be linked in. All Standard C++ headers include <use_ansi.h>: if you include any Standard C++ header in your application, the Standard C++ library will be linked by default.

      |-------------------------------------------------|
      |             Standard C++ Headers                |
      |-------------------------------------------------|
      | ALGORITHM | BITSET    | COMPLEX    | DEQUE      |
      | EXCEPTION | FSTREAM   | FUNCTIONAL | IOMANIP    |
      | IOS       | IOSFWD    | IOSTREAM   | ISTREAM    |
      | ITERATOR  | LIMITS    | LIST       | LOCALE     |
      | MAP       | MEMORY    | NUMERIC    | OSTREAM    |
      | QUEUE     | SET       | SSTREAM    | STACK      |
      | STDEXCEPT | STREAMBUF | STRING     | STRSTREAM  |
      | TYPEINFO  | UTILITY   | VALARRAY   | VECTOR     |
      |-------------------------------------------------|
				

You cannot mix calls to the old iostream library and the new Standard C++ library.

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Q3: How do I retain the old iostream functionality if I port my project from an earlier version of Visual C++?

A3: If you want to retain the old iostream library, include one or more of the old iostream header files in your code. Do not use the new Standard C++ headers. You cannot mix calls to the old iostream library and the new Standard C++ library.

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Q4: How do I make the Standard C++ Libraries the default libraries for my application?

A4: If you want to make the Standard C++ Libraries the default, include one or more of the new Standard C++ headers. Remember, you cannot mix calls to the old iostream and the new Standard C++ library. Existing libraries (static or dynamic link) that use old iostream functions will have to be modified to use Standard C++ library iostream functions.

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Q5: I want to use Standard C++ Libraries in a Microsoft Foundation Classes (MFC) application. Will this cause any conflicts with the C-Runtime Libraries?

A5: No. MFC does not use any C-Runtime functions that will conflict with the Standard C++ Libraries.

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Q6: Why do I get error "error C2065: 'cout' : undeclared identifier" even though I have included <iostream>?

A6: Standard C++ library is implemented in its own namespace "std". Make sure to add the statement

using namespace std;
				

in the beginning of your program or to qualify each Standard C++ library identifier with namespace std, for example, std::cout.

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Q7: Why am I getting "compiler error C2371: 'identifier' redefinition; different basic types"?

A7: Mixing Standard C++ headers and old iostream headers will cause this error, even if they are included in different source files. The following are the different headers:

      |-------------------------|
      |  Old iostream Headers   |
      |-------------------------|
      | FSTREAM.H  | IOMANIP.H  |
      | IOS.H      | IOSTREAM.H |
      | ISTREAM.H  | OSTREAM.H  |
      | STDIOSTR.H | STREAMB.H  |
      | STRSTREA.H |            |
      |-------------------------|

	  
      |-------------------------------------------------|
      |             Standard C++ Headers                |
      |-------------------------------------------------|
      | ALGORITHM | BITSET    | COMPLEX    | DEQUE      |
      | EXCEPTION | FSTREAM   | FUNCTIONAL | IOMANIP    |
      | IOS       | IOSFWD    | IOSTREAM   | ISTREAM    |
      | ITERATOR  | LIMITS    | LIST       | LOCALE     |
      | MAP       | MEMORY    | NUMERIC    | OSTREAM    |
      | QUEUE     | SET       | SSTREAM    | STACK      |
      | STDEXCEPT | STREAMBUF | STRING     | STRSTREAM  |
      | TYPEINFO  | UTILITY   | VALARRAY   | VECTOR     |
      |-------------------------------------------------|
				

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Q8: I have a project that was built with the "Ignore Default Libraries" option (/NOD or /NODEFAULTLIB). With Visual C++ 5.0 or later, I am getting linker error "LNK2001: unresolved external symbol 'symbol' ;" on all iostream function calls. What has changed?

A8: The iostream functions have been removed from the C-Runtime library.

If you are using the old iostream functions, you must add an additional library as follows: LIBCI.lib (single-threaded <ML>), LIBCIMT.lib (multithreaded <MT>), or MSVCIRT.lib (multithreaded dll <MD>).

If you are using the new iostream functions included with the Standard C++ library, you must add an additional library as follows: LIBCP.lib (single-threaded <ML>), LIBCPMT.lib (multithreaded <MT>), or MSVCPRT.lib (multithreaded dll <MD>).

Do not mix different versions of the libraries. For example, if you are using the single-threaded version of the C-Runtime library, you must also use the single-threaded version of the old iostream library or Standard C++ library.

You cannot mix calls to the old iostream library functions and the new Standard C++ library iostream functions.

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Q9: I am getting compiler warnings C4786 and/or C4788. None of the symbols in my program is anywhere near 255 characters in length. What is causing this?

A9: C4786/C4788 is issued when a symbol's name exceeds 255 characters in length. This often happens with template class, and STL uses template class extensively.

Ignoring this warning is usually safe. Use a #pragma warning (disable: 4786,4788) to suppress the messages.

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Q10: I am getting compiler warning "C4530: C++ exception handler used, but unwind semantics are not enabled. Specify -GX." What does this mean?

A10: Programs that use the Standard C++ library must be compiled with C++ exception handling enabled. C++ exception handling can be enabled by:

• Selecting the Enable exception handling option in the C++ Language Category of the C/C++ tab in the Project Settings dialog box. -or-
  
  
• Using the /GX compiler switch.

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Q11: I am getting compiler error C2146, followed by C2065, and finally C2143, all pointing to the same line in my source. What does this mean?

A11: This sequence of errors can be caused by the following type of construct:

vector<int, allocator<int>>iV;
				

The problem is caused by the consecutive ">>" at the end of the declaration. The solution is to put a space between two characters, so the construct becomes:

vector<int, allocator<int> > iV;
				

This is consistent with the proposed ANSII specification.

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