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<title>The GNU Fortran Compiler: About GNU Fortran</title>
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<a name="About-GNU-Fortran"></a>
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<p>
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Next: <a href="GNU-Fortran-and-GCC.html#GNU-Fortran-and-GCC" accesskey="n" rel="next">GNU Fortran and GCC</a>, Up: <a href="Introduction.html#Introduction" accesskey="u" rel="up">Introduction</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
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<a name="About-GNU-Fortran-1"></a>
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<h3 class="section">1.1 About GNU Fortran</h3>
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<p>The GNU Fortran compiler supports the Fortran 77, 90 and 95 standards
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completely, parts of the Fortran 2003 and Fortran 2008 standards, and
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several vendor extensions. The development goal is to provide the
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following features:
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</p>
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<ul>
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<li> Read a user’s program,
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stored in a file and containing instructions written
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in Fortran 77, Fortran 90, Fortran 95, Fortran 2003 or Fortran 2008.
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This file contains <em>source code</em>.
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</li><li> Translate the user’s program into instructions a computer
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can carry out more quickly than it takes to translate the
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instructions in the first
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place. The result after compilation of a program is
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<em>machine code</em>,
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code designed to be efficiently translated and processed
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by a machine such as your computer.
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Humans usually are not as good writing machine code
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as they are at writing Fortran (or C++, Ada, or Java),
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because it is easy to make tiny mistakes writing machine code.
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</li><li> Provide the user with information about the reasons why
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the compiler is unable to create a binary from the source code.
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Usually this will be the case if the source code is flawed.
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The Fortran 90 standard requires that the compiler can point out
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mistakes to the user.
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An incorrect usage of the language causes an <em>error message</em>.
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<p>The compiler will also attempt to diagnose cases where the
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user’s program contains a correct usage of the language,
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but instructs the computer to do something questionable.
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This kind of diagnostics message is called a <em>warning message</em>.
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</p>
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</li><li> Provide optional information about the translation passes
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from the source code to machine code.
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This can help a user of the compiler to find the cause of
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certain bugs which may not be obvious in the source code,
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but may be more easily found at a lower level compiler output.
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It also helps developers to find bugs in the compiler itself.
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</li><li> Provide information in the generated machine code that can
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make it easier to find bugs in the program (using a debugging tool,
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called a <em>debugger</em>, such as the GNU Debugger <code>gdb</code>).
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</li><li> Locate and gather machine code already generated to
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perform actions requested by statements in the user’s program.
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This machine code is organized into <em>modules</em> and is located
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and <em>linked</em> to the user program.
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</li></ul>
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<p>The GNU Fortran compiler consists of several components:
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</p>
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<ul>
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<li> A version of the <code>gcc</code> command
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(which also might be installed as the system’s <code>cc</code> command)
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that also understands and accepts Fortran source code.
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The <code>gcc</code> command is the <em>driver</em> program for
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all the languages in the GNU Compiler Collection (GCC);
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With <code>gcc</code>,
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you can compile the source code of any language for
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which a front end is available in GCC.
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</li><li> The <code>gfortran</code> command itself,
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which also might be installed as the
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system’s <code>f95</code> command.
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<code>gfortran</code> is just another driver program,
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but specifically for the Fortran compiler only.
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The difference with <code>gcc</code> is that <code>gfortran</code>
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will automatically link the correct libraries to your program.
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</li><li> A collection of run-time libraries.
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These libraries contain the machine code needed to support
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capabilities of the Fortran language that are not directly
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provided by the machine code generated by the
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<code>gfortran</code> compilation phase,
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such as intrinsic functions and subroutines,
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and routines for interaction with files and the operating system.
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</li><li> The Fortran compiler itself, (<code>f951</code>).
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This is the GNU Fortran parser and code generator,
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linked to and interfaced with the GCC backend library.
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<code>f951</code> “translates” the source code to
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assembler code. You would typically not use this
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program directly;
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instead, the <code>gcc</code> or <code>gfortran</code> driver
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programs will call it for you.
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</li></ul>
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<hr>
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<div class="header">
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<p>
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Next: <a href="GNU-Fortran-and-GCC.html#GNU-Fortran-and-GCC" accesskey="n" rel="next">GNU Fortran and GCC</a>, Up: <a href="Introduction.html#Introduction" accesskey="u" rel="up">Introduction</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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