Intel® Visual Fortran, part of the Intel® Parallel Studio XE developer toolset, integrates with Microsoft developer tools with the goal of providing outstanding application performance on Intel processors as well as with compatible processors from other manufacturers. Intel Visual Fortran is a full-language Fortran 2003 compiler with many Fortran 2008 features plus a wide range of popular industry extensions.
Intel Visual Fortran is the successor to Compaq* Visual Fortran (CVF) and comes from the same development team. Intel Visual Fortran is highly compatible with CVF and for most customers. migrating is easy. This article will lead you through the process.
In most cases, you can rebuild existing CVF applications with the new compilers without source changes, but some applications may need minor coding changes, and build methods may need minor adjustments. This article describes the key differences you are likely to encounter. For additional details, refer to the appropriate compiler release notes and the compiler documentation.
If you already have installed a supported version of Microsoft Visual Studio, Intel Visual Fortran will integrate into that Visual Studio development environment allowing you to create, build and debug Fortran and mixed-language applications. If you do not have a supported version of Microsoft Visual Studio installed, Intel Visual Fortran will install Microsoft Visual Studio Shell to provide a rich development environment for Fortran programming on IA-32 and Intel® 64 systems. (Note that some license types of Intel Visual Fortran do not provide Microsoft Visual Studio Shell. Please read the compiler's System Requirements for details.)
The Intel Visual Fortran product can coexist on a system with CVF, and you can continue using the older product if you wish. However, Intel Visual Fortran does not integrate with Microsoft Visual Studio 6 environment used by CVF, whereas CVF does not integrate with the newer versions of Microsoft Visual Studio. The Intel and Compaq products install into separate folder trees and use separate registry variables.
All Fortran sources must be recompiled with Intel Visual Fortran; you cannot use CVF-compiled objects, modules, or static libraries with Intel Visual Fortran. You can, however, use CVF-built dynamic link libraries (DLLs) with applications compiled with the Intel Visual Fortran Compiler, as long as you do not try to share input/ output units across the two environments. Note also that third-party libraries built for use with CVF may not work with Intel Visual Fortran . Contact the library supplier for more information.
Intel Visual Fortran supports all of the CVF language syntax, including extensions from Digital Equipment Corporation (DEC) Fortran and Microsoft Fortran PowerStation* 4. All CVF library routines are supported, including those from the QuickWin and Portability libraries, as are all of the system-interface modules. In most cases, a simple rebuild of the application with the Intel compiler is all that is needed. Source changes that you may need to make are described below.
Features Not Supported
Intel Visual Fortran supports all of the language syntax supported by CVF. However, some of the CVF product features are not supported by Intel Visual Fortran. These include the following:
- Compaq Extended Math Library. The Intel® Math Kernel Library or third-party libraries such as IMSL* and NAG* may be suitable alternatives. (Intel Math Kernel Library is provided with Intel Visual Fortran and the IMSL library is provided with Intel Parallel Studio XE for Fortran Windows with IMSL or can be purchased as an add-on to an Intel Parallel Studio XE 2015 (or later) installation that includes Fortran. Other products must be obtained separately.)
- Format editor tool.
- Save Fortran Environment tool.
If you have existing applications that were created by the CVF COM Server Wizard, you may be able to rebuild them with Intel Visual Fortran. If you need to make changes to the interfaces, you can do so in CVF if you have left it installed. CVF COM Server Wizard projects cannot be converted to Intel® COM Server Wizard projects.
Although Intel Visual Fortran supports all CVF language syntax, incorrect programs which were compilable with CVF may result in error messages when compiled with Intel Visual Fortran. If you encounter unexpected error messages and need assistance resolving them, please see Getting Help
Some applications may be affected by changes in defaults:
- Unlike CVF, the Intel Fortran compiler can check for mismatches in argument lists across multiple source files, unlike CVF which did this only within a single source file. You may see more error messages when the program is built with Intel Fortran due to this enhanced checking. If you need help understanding a particular error message, search for it on the Intel Developer Zone web site or ask for help in the user forum. As a last resort, you can disable this enhanced checking by disabling the options /gen-interface (Fortran > Diagnostics > Generate Interface Blocks) and /warn:interface (Fortran > Diagnostics > Check Routine Interfaces).
- In CVF, the default for local variables in procedures was that SAVE semantics were assumed. This caused the compiler to allocate local variables in static storage, which had the side-effect of these variables usually having an initial value of zero, though this was not guaranteed. The Intel Fortran compiler defaults to /auto-scalar, which means that scalar variables are allocated on the stack by default, while arrays and derived types are still allocated statically. If your program assumed that a local variable was preserved across calls or that it was initially zero, this can cause incorrect run-time behavior. The solution is to add a SAVE declaration for variables that should be preserved, and/or to add initialization where required. To revert to the CVF semantics, add the option /Qsave (in Visual Studio, this is property Fortran > Data > Local Variable Storage > All variables SAVE. As of version 11, projects converted from CVF projects have /Qsave added by default.
- In CVF, floating point arithmetic was always done using the "X87" instructions, which could lead to inconsistent values of expressions depending on optimizer choices. As of version 11, Intel Fortran uses the SSE2 instructions by default, which is faster and more consistent, but may give different results for some computations. If you see this issue, try setting the option /fp:source (Fortran > Floating Point > Floating Point Moel > Source). If that does not resolve the issue, specify that the X87 instructions are to be used by specifying /arch:ia32 (Fortran > Code Generation > Enable Enhanced Instruction Set > No enhanced instruction sets)
Microsoft Visual Studio Shell*
If you are using Microsoft Visual Studio Shell, the following limitations apply:
- No Microsoft language processors such as Visual C++* or Visual BASIC* are supplied.
- CVF projects cannot be converted to Intel Visual Fortran projects. Instead, create a new Intel Visual Fortran project and add your sources to it.
- The Microsoft Visual C++ Resource Editor, used to create and edit dialog boxes, icons and version resources, is not provided due to licensing restrictions. A freeware alternative is ResEdit from www.resedit.net. If you have existing resource files, they can be used
- The Intel® C++ Compiler cannot be used in this environment.
These limitations do not apply when using a retail edition of Microsoft Visual Studio, or if using Microsoft Visual Studio Community Edition.
Converting CVF Projects
Intel Visual Fortran includes project-conversion wizards to make it easy to migrate from CVF. Note that the project conversion wizards are not available if you are using Microsoft Visual Studio Premier Partner Edition.
Conversion is a two-step process:
1. Open the CVF workspace in Visual Studio by right-clicking on the workspace's .DSW file and selecting Open With... Microsoft Visual Studio 20xx. You will see a message similar to the following:
Figure 1. Initial Project Conversion Dialog
Click Yes To All to convert each project to a Visual C++ project in a "solution" (similar to a workspace).
2. In the right or left pane, you will see the Solution Explorer with the project(s) present. If you do not see the Solution Explorer pane, select View>Solution Explorer. At this point, the conversion to Fortran project(s) is not yet complete. For each project, right-click the project name and select Extract Compaq Visual Fortran Project Items.
Figure 2. Extract Fortran Project Items Dialog
The project will now be converted.
Figure 3. Converted Project
If the CVF project contains both Fortran and C sources, it must be converted into two single-language projects under a solution - one builds a static library and the other links to that library - because Microsoft Visual Studio does not allow multiple languages in a single project. The project conversion wizard asks you which language has the main (linkable) project, Fortran or C, and makes the appropriate adjustments. Figure 4 is an example of converting a mixed-language project.
Figure 4. Mixed Language Project Dialog Box
In this example, the main (executable) program is in C, so we select "The Visual C++ Project".
After conversion, the mixed-language project looks like Figure 5.
Figure 5. Converted Mixed Language Project
In the prior example, the CVF NODLL project was split into a C++ executable project named NODLL and an Intel Fortran static library project NODLL_lib. The conversion wizard automatically makes NODLL_lib a dependent of NODLL, so that the library is built first and then is linked into the C code.
If you convert a CVF project, the conversion wizard will change project settings from the default to enhance compatibility with CVF. An important change is the default calling convention: if it was "Default" in CVF, the conversion wizard changes it to "CVF." (The following section provides more information on calling conventions.) Unless you had a mixed-language application that depended on CVF-specific calling conventions, you should set the default calling convention back to the default, in most cases.
If your mixed-language project was a static library project, two static library projects will be created, one a dependent of the other. Visual Studio will automatically combine the child library with the parent when the solution is built.
Getting Used to the Microsoft Visual Studio IDE
The Microsoft Visual Studio Integrated Development Environment (IDE) is somewhat different from the one shared by CVF and some users may at first find it difficult to perform common tasks. This paper covers some of the major changes, but it is not comprehensive. For more information on using the IDE, see the MSDN Library* documentation that accompanies Microsoft Visual Studio. (If you are using Microsoft Visual Studio Shell, you can access the MSDN Library at http://msdn2.microsoft.com/en-us/library)
Projects and Solutions
In CVF (and Visual C++ 6.0), "projects" were placed in "workspaces." A CVF workspace was little more than a container for one or more projects and was not involved in the build process. A project built something (an EXE, LIB or DLL file in most cases), and it could contain both Fortran and C code. One project was always designated as "active."
In Visual Studio, projects are substantially the same, but a project can be associated with only one language. For example, if you add C files to a Fortran project, the C files will be ignored. A solution holds multiple projects, but it is different from a workspace because you can build a solution, which builds all of the contained projects in a specified, user-configurable order.
When you have a mixed Fortran and C application, you must put the Fortran code into a Fortran project and the C code into a C (or C++) project. The projects get built separately and then, if appropriate, they are linked together. If the old project was a static library, two static library projects are created, with the objects going into a combined .LIB file. In this case, it does not matter which project you select as being the "main" project.
Changing settings in the new Visual Studio environment is different as well. Instead of a tabbed dialog box for Settings, there is a tree-view set of "Property Pages." Figure 6 shows a set of property pages for an example project.
Figure 6. Property Pages
In this example, the Fortran General Property Page is displayed. Current property values that are the defaults are shown bolded, and a brief description of the highlighted property is displayed at the bottom of the pane.
To change a property value that has specific options, click on the value. An arrow icon displays to the right of the value.
Figure 7. Changing a Property
Click on the arrow to display the options and select the desired option. Properties that offer a list of items, such as Additional Include Directories in the example above, display a list icon (three dots).
3. Click the icon to open a separate dialog box, where you can enter the values. If you have only one value, type it directly on the Property page. You can directly type properties that are a single text string. In some cases, an arrow icon is available to allow you to select "Inherit from project defaults."
Debugging with Intel Visual Fortran is similar to using CVF, but some of the controls are in different places.
- To set a breakpoint, click in the left margin next to a statement; the red Stop icon displays. As with CVF, you must set at least one breakpoint, otherwise the program will run to completion when debugging starts.
- To execute under the debugger, click the green triangle "Play" icon next to the configuration name.
Unlike in CVF, there is not a default button on the toolbar for "Start Without Debugging". You can access this function by selecting it under the Debug menu or by pressing Ctrl+F5. If you want to add the button, select Tools>Customize. In the Commands tab, select Debug under Categories and drag the Start Without Debugging button to the toolbar.
Figure 8. Setting a Breakpoint
While Intel has taken great care to avoid the need for source changes to permit "rebuild and go," a number of implementation differences between the Intel and Compaq compilers necessitate making changes for selected applications. For the latest information on changes, please refer to the Intel Visual Fortran Compiler Release Notes.
While the part of the compiler that handles Fortran syntax and semantics, often referred to as the "front end," is derived from CVF, improvements have been made in detecting incorrect usage, and you may find that the new compiler issues diagnostic messages
for certain usages where the older compiler did not. For example, the compiler now gives an error for a source that makes a call to a non-pure intrinsic such as RANDOM_NUMBER from inside a pure procedure. In such cases, you will need to correct the coding errors. If you believe a diagnostic is inappropriate, please see Getting Help.
Default Calling Conventions Have Changed
In CVF, the default calling mechanism was STDCALL, and routine names were ‘decorated ' by adding @n to the end, where n was the number of bytes of argument list. Intel Visual Fortran Compiler adopts the more common C calling mechanism used by versions 7.1 and earlier of the Intel Fortran Compiler. Routine names are still converted to uppercase by default, and a leading underscore is added, but there is no @n suffix.
Another change is the manner in which CHARACTER argument lengths are passed. In CVF, these were passed immediately following the address of the CHARACTER item, but in Intel Visual Fortran, all the lengths are passed at the end of the argument list. In other words, the default has changed from /iface: mixed_str_len_arg to /iface:nomixed_str_len_arg.
If you have a Fortran-only application, this change may not be important to you. If, on the other hand, you have a mixed-language application, you need to be aware of the impact of the change in compiler default. You can tell the compiler to use the CVF default on the External Procedures property page, or with the /iface:cvf command-line switch.
A special case where the convention change matters is if your application uses "callback procedures". This is where you pass a routine name from your program as an argument to a library routine. Some kinds of library routines which use callbacks are Windows API and IMSL libraries, the QSORT routine from the Intel Fortran Portability Library, and also the USEROPEN keyword of the Fortran OPEN statement. Callback routines assume a specific calling convention and if there is a mismatch it can cause stack corruption and unpredictable results.
The Windows API always uses the STDCALL convention, so if you are passing Fortran routines to Windows API routines, be sure to add the directive
!DEC$ ATTRIBUTES STDCALL,REFERENCE :: routine-name
to the callback routine. Most other uses of callbacks, including the IMSL library, assume the compiler 's default conventions. If you encounter unexpected run-time errors, try setting the calling convention to "Default" to see if that resolves the issue.
GETARG, IARGC and NARGS Are Now Intrinsic
The command-line inquiry routines GETARG, IARGC and NARGS are now recognized as intrinsic procedures by the compiler. If your application source declares any of these names as EXTERNAL or provides an explicit procedure interface for them, you must remove those declarations to prevent link-time errors.
New Module Names for System and Library Declarations
Compaq Visual Fortran provided modules with definitions of Windows* API routines and symbols, as well as modules for Fortran library routines. These modules had names such as DFWIN, DFLIB, etc. Intel Visual Fortran provides compatible modules with the same names, but these are wrappers around modules with new names. You do not need to change your sources, but you should begin using the new names in new development. In DFLIB, symbols have been relocated into one of three new modules: IFCORE, IFPORT and IFQWIN.
You may find it useful to select the specific module containing the symbols you are interested in.
|Old Name||New Name||Description|
|DFCOM||IFCOM||COM and OLE|
|DFCOMTY||IFCOMTY||Obsolete, use IFWINTY|
|DFLIB||IFCORE, IFPORT, IFQWIN||General library, Portability library, QuickWin|
|DFLOGM, DFLOGMT||IFLOGM, IFLOGMT||Dialogs|
|DFMT||IFMT||Multithread routines (obsolete)|
|DFNLS||IFNLS||National language support|
|DFOPNGL, DFOPNGLT||IFOPNGL, IFOPNGLT||OpenGL*|
|DFWBASE||IFWBASE||Deprecated WIN16 routines (not supported on 64-bit architectures|
|DFWIN||IFWIN||Win32 APIs (use of individual modules such as KERNEL32 is recommended instead)|
|DFWINA||IFWINA||Renamed Win32 routines that conflict with QuickWin names|
|DFWINTY||IFWINTY||Win32 API types and constants|
The individual Windows API modules such as KERNEL32 have the same names as in CVF. Note that new Win32 modules, such as PSAPI, have been added.
In most cases, you will not need to make changes in your build procedures. However, to provide for compatibility with future versions of Intel Fortran compilers, some changes are recommended. This section describes differences that affect building applications.
Compile Command is Now ifort
Under CVF, four command names were provided for invoking the compiler: df, f90, f77 and fl32. df and f90 were equivalent, f77 added options for compatibility with Compaq Fortran 77,and fl32 added options for compatibility with Microsoft Fortran PowerStation. In Intel Visual Fortran, ifort is the command name to invoke the compiler.
If you leave CVF installed on your system, it coexists with Intel Visual Fortran. When using the command line, be sure to use the appropriate shortcut in the Start menu to start your command session. For CVF, use "Fortran Command Prompt." For Intel Visual Fortran , use one of the selections under Intel Parallel Studio XE > Command Prompt. Each of these will establish the proper environment for the selected compiler. The IDEs are separate and do not interfere with each other.
Using the IMSL* Fortran Libraries from Rogue Wave Software*
Compaq Visual Fortran Professional Edition included the IMSL* 5.0 Fortran Numeric Library from Visual Numerics* (now Rogue Wave Software.) For use with Intel Visual Fortran, we offer IMSL 7.0, either combined with Fortran or as an "add-on" to larger Intel Parallel Studio XE packages that include Fortran. In addition to many new and updated routines, the new version adds the following features not included in Compaq Visual Fortran Professional Edition:
- Multithreaded libraries for improved performance on multi-core and multiprocessor systems..
- DLL form of the libraries.
- Support for the Intel® 64 architecture
- New, unified interface modules making use of Fortran 95 generic interfaces and optional arguments.
The IMSL libraries are installed separarely from the compiler. Please be sure to install the compiler first.
An existing application that uses the IMSL libraries will need few or no changes, unless you want to take advantage of the new features. You will need to make a change in how the application is built to reference the proper libraries. Below is an overview of this change. See the Intel Visual Fortran Compiler on-disk documentation under Building Applications, Using Libraries for additional details.
A change that may be needed is if your calls to the IMSL library pass callback routines. These are often used to evaluate user functions in "solver" routines. You must make sure that your callback routines use the default calling convention and not CVF 's STDCALL. See the above section on the change in calling conventions for more information.
Locating and Referencing the IMSL Libraries
In Compaq Visual Fortran, there was just one set of IMSL libraries: static and non-threaded. In Intel Visual Fortran with IMSL, there are four sets of libraries with different names. Rather than explicitly list the libraries, as was commonly done with CVF, you should instead specify the path to the folder containing the libraries and use one of the supplied INCLUDE files to create a reference to the specific libraries required.
For details on how to specify the IMSL libraries, please see Installing and using the IMSL* Libraries
For additional options and details, please refer to the Building Applications manual on-disk documentation section on using the IMSL libraries (Building Applications > Using Libraries > Using the IMSL* Mathematical and Statistical Libraries).
Intel Visual Fortran provides a rich feature set:
- Full support of Intel multi-core processors and 64-bit architectures
- Full Fortran 2003, and many Fortran 2008 language features
- Quadruple-precision floating point REAL(16) and COMPLEX(32)
- Automatic parallelization
- OpenMP* support
- Advanced optimization for new Intel processors
For more information on these and other features, see the compiler Release Notes.
If you have questions about using Intel Visual Fortran, please ask in our User Forum.