I am working on a project that was given to me by someone else. This project compiles using the ifort compiler and contains a ton of fortran .FOR files written in seemingly free- format. Recently I have been studying fortran code formats in a little more detail and came accross this article which states:
".f90 specifies Fortran free-form source and .f, .ftn, or .for specify fixed-form souce"
I don't understand why and how these .FOR files can compile OK if they are written in free form, and if ifort recognizes them as fixed form. Could anyone please fill me in on this? I'm trying to migrate this project to gfortran so I'm very confused. Also I do not want to change everything to .f90 files because I am worried this might break something else.
Free form source code can be stored and compiled in files with various extensions. If it is not the default extension, the compiler must be instructed to treat it as fixed form.
In Intel Fortran such flag is -free or the Windows equivalent /Qfree. In gfortran it is -ffree-form, so
gfortran -ffree-form source.for
compiles the .for file as free form.
Related
I have a bunch of Fortran77 code that I need to use for my research but I'm having trouble compiling it to run on my MacBook so I turned to Julia. I'm new to the language but for the life of me I can't figure out how to execute a Fortran script directly in Julia. All I want is to have a program that runs a F77 script and hands control directly to Fortran. I would just rewrite it with Julia or Numpy but there's about 10,000 lines of code and less than 200 lines of comment and I don't have time for that.
It seems from the wording of your question like you want to use Julia to directly call Fortran "scripts" – presumably Fortran .f source files – is that accurate?
As others have indicated in the comments, Fortran is not a scripting language: you cannot directly execute Fortran source files; instead you must use a Fortran compiler (e.g. gfortran, ifort) to translate Fortran programs into native libraries or executables for the system you want to run programs on. Julia will not help with this in any way as Julia is not a Fortran interpreter or compiler – it can neither run Fortran code directly nor convert Fortran source files into executables/libraries.
If, however, you already have a Fortran shared library compiled (.so file on Linux, .dylib on macOS, .dll on Windows), you can call it easily from Julia, as described in Integrating Fortran code in Julia. If you can compile Fortran source code to an executable (as opposed to a shared library), then you do not need anything else to run it – executables, by definition, are standalone.
Most projects in compiled languages like Fortran or C/C++ come with Makefiles or other mechanisms to help invoke a compiler to generate the appropriate binary artifacts (executables and/or libraries).
I'm a C++ beginner and I'm studying the basics of the language. There is a topic in my book about the compiler and my problem is that I can not understand what the text wants to say:
C++ is a compiled language so you need to translate the source code in
a file that the computer can execute. This file is generated by the
compiler and is called the object code ( .obj ), but a program like
the "hello world" program is composed by a part that we wrote and a part
of the C++ library. The linker links these two parts of a program and
produces an executable file ( .exe ).
Why does my book tell that the file that is executed by the computer is the one with the obj suffix (the object code) and then say that it is the one with the exe suffix?
Object files are source compiled into binary machine language, but they contain unresolved external references (such as printf,for instance). They may need to be linked against other object files, third party libraries and almost always against C/C++ runtime library.
In Unix, both object and exe files are the same COFF format. The only difference is that object files have unresolved external references, while a.out files don't.
The C++ specification is a technical document in English. For C++11 have a look inside n3337 (or spend a lot of money to buy the paperback ISO standard). In theory you don't need a computer to run a C++ program (you could use a bunch of human slaves, but that would be unethical, inefficient, and unreliable).
You could have a C++ implementation which is an interpreter, not a compiler (e.g. Ch by SoftIntegration)
If you install Linux on your laptop (which I recommend doing to every student) then you could have several free software C++ compilers, in particular GCC and Clang/LLVM (using g++ and clang commands respectively). Source files are suffixed .cc, or .cxx, or .cpp, or even .C (I prefer .cc), and you could ask the compiler to handle a file of some other suffix as a C++ source file (but that is not conventional). Then, both object files (suffixed .o) and executables share the same ELF format. Conventionally, executables don't have any suffix (e.g. g++ is a binary executable, not doing much except starting other processes like cc1plus -the compiler proper-, as -the assembler-, ld -the linker- etc...)
In all cases I strongly recommend:
to enable all warnings and debug info during compilation (e.g. use g++ -Wall -g ....)
to improve your source code till you got no warnings
to learn how to use the debugger (gdb)
to be able to build your program on the command line
to use a version control system like git
to use a good editor like emacs, gedit, geany, or gvim
once you are writing programs in several source files, learn how to use a builder like make
to learn C++11 (or even perhaps C++14) rather than older C++ standards
to also learn other programming languages (Ocaml, Scheme, Haskell, Prolog, Scala, ....) since they would improve your thinking and your way of coding in C++
to study the source code of several free software coded in C++
to read the documentation of every function that you are using, e.g. on cppreference or in man pages (for Linux)
to understand what is undefined behavior (the fact that your program sometimes work does not make it correct).
Concretely, on Linux you could edit your Hello World program (file hello.cc) with gedit or emacs (with a command like gedit hello.cc) etc..., compile it using g++ -Wall -g hello.cc -o hello command, debug it using gdb ./hello, and repeat (don't forget to use git commands for version control).
Sometimes it makes sense to generate some C++ code, e.g. by some shell, Python, or awk script (or even by your own program coded in C++ which generates C++ code!).
Also, understand that an IDE is not a compiler (but runs the compiler for you).
The basic steps for creating an application from a C or C++ source file are as follows:
(1) the source files are created (by a person or generated by a program), (2) the source files are compiled (which is really two steps, Preprocessor and compilation) into object code, (3) the object files that are created by the C/C++ compiler are linked to create the .exe
So you have these steps of transforming one version of the computer program, the source files, to another, the executable. The C++ source is compiled to produce the object files. The object files are then linked to produce the executable file.
In most cases there are several different programs involved in the compile and link process with C and C++. Each program takes in certain files and creates new files.
C/C++ Preprocessor takes in source code files and generates source code files
C/C++ Compiler takes in source code files and generates object code files
the linker takes in object code files and libraries and generates executable files
See What is the difference between - 1) Preprocessor,linker, 2)Header file,library? Is my understanding correct?
Most compiler installations have a program that runs these various applications for you. So if you are using gcc then gcc program will run first the C++ Preprocessor then then C++ compiler and then the linker. However you can modify what gcc does with command line options to tell it to only run the C++ Preprocessor or to only compile the source files but not to link them or to only link the object code files.
A brief history of computer languages and programming
The languages used for programming computers along with the various software development tools have evolved over the years.
The first computers were programmed with numbers entered by switches on a console.
Then people started developing languages and software that could be used to create software more easily and quicker. The first major development was creating assembler language where each line of source was converted by a computer program into a machine code instruction. Along with this came the development of linkers (which link pieces of machine code together into larger pieces). Assemblers were improved by adding a macro or preprocessor facility somewhat like the C/C++ Preprocessor though designed for assembly language.
Then people created programming languages that looked more like people written languages rather than assembler (FORTRAN and COBOL and ALGOL for instance). These languages were easier to read and a single line of source might be converted into several machine instructions so it was more productive to write computer programs in these languages rather than assembler.
The C programming language was a later refinement using lessons learned from the early programming languages such as FORTRAN. And C used some of the same software development tools that already existed such as linkers which already existed. Still later C++ was invented, starting off as a refinement of C introducing object oriented facilities. In fact the first C++ compiler was really a C++ translator which translated C++ source code to C source code which was then compiled with a C compiler. However modern C++ is compiled straight to machine code in order to provide the full functionality of the C++ standard with templates, lambdas, and all the other things with C++11 and later.
linkers and loaders
When you run a program you run the executable file. The executable file contains several kinds of information. The first is the machine instructions that are the result of compiling the C++ source code. The other is information that the loader uses in order to know how to load the executable into memory.
In the old days, long long ago all libraries and object files were linked together into an executable file and the executable file was loaded by the loader and the loader was pretty simple.
Then people invented shared libraries and dynamic link libraries and this required the linker to be more complex and the loader to be more complex.
The linker became more complex because it had to be able to recognize the difference between using a shared library and a static library and be able to generate an executable file that not only contains the linked object code but also information for the loader about any dynamic libraries.
The loader became more complex because not only does the loader have to load the executable file into memory so that it can start running, the loader must also find any shared libraries or dynamic link libraries that are also needed and load those too. And the loader also has to do a certain amount of linking of the additional components, the shared libraries, so the loader does a lot more than it used to do.
See also
Difference between shared objects (.so), static libraries (.a), and DLL's (.so)?
What is an application binary interface (ABI)?
How to make a SIMPLE C++ Makefile
Object code (within an object file): Output from a compiler intended as input for a linker (for the linker to produce executable code).
Executable: A program ready to be run (executed) on a computer
I installed the intel c++ compiler, and sourced the compilervars.h file. (I think this is how you are supposed to set up the compiler).
When testing a simple HelloWorld! program compiling with the icpc command for bot the .cpp and .o files I am told that there is no /bits/c++config.h file. The file is not located under /usr/include/c++/4.8/bits or /usr/include/c++/4.8.1/bits. I have read up on this problem (there were a few threads about it) but could not figure out how to fix it.
I got the program to compile by using gcc for the .cpp file and icpc for the .o file. gcc won't compile the .o file and icpc won't compile the .cpp file.
I am a rookie to setting up programming environments because I mostly have just programmed via shh on school computers. Any help would be greatly appreciated.
This shall be fixed by adding corresponding -I option to your compiling command. If your machine is x32, try something like
-I/usr/include/i386-linux-gnu/c++/4.8/
or
-I/usr/include/x86_64-linux-gnu/c++/4.8/
for x64 machine.
Does C++ code compile to assembly code? If we have C++ code, will we be able to get assembly code?
The vast majority of C++ compilers will convert the C++ source into object files (machine code with enough control information to be linked into an executable). They may actually generate assembly language as an interim step and even use a separate assembler for processing the assembler source, but you'll generally never see that. For example, you have to actually go out of your way to get gcc to generate assembly code (.s file) by using the -S flag. Normally, you would never see the assembly.
But the C++ standard doesn't mandate the final form that's output from the compiler, just that the code has to behave in a certain way when you run it.
In fact, the earliest C++ "compilers" actually generated C source code and then compiled that.
You can have your C++ compiler generate object code, Java byte code, or even GWBASIC, should you be feeling masochistic.
Your code has to be understood by the machine, and, as it is not interpreted nor running in a VM, it is first transformed in assembly. You can get this assembly code by using the -S flag in your g++ compile options (as long as you are using g++ of course).
g++ -S -o file.s file.cpp
should do the trick.
It depends on the compiler. There are no real rules regarding what C++ compiles into, except at some point it should be able run on a computer. Most compilers have a switch to compile to assembly.
With gcc you can add -S to compile into a .asm file.
For visual studio see: http://codegem.org/2008/10/generate-assembly-from-c-code-in-visual-studio
We have recently downloaded, installed and compiled gcc-3.0.4 code. gcc compiler has built successfully and we where able to compile some same test cpp file. I would like to know how we can modify gcc source code so that we add additional run time debugging statements like the binary in execution compiled by my gcc should print below statement in a log file:
filename.cpp::FunctionName#linenumber-statement
or any additional information that I can insert via this tailored compiler code.
Have you looked at the macros __FILE__ and __LINE__? They do that for you without modifying the compiler. See here for more information.
My general understand of the GCC architecture is, that it is divided into front-end (parser), middle (optimization in a special intermediate language), and a back-end (generating platform dependent output). So, for your purposes you would have to look into the back-end part.
Don't do that with an ancient compiler like GCC 3.0.
With a recent GCC 4.9 (in end of 2014 or january 2015) you could customize the compiler, e.g. with a MELT extension, which would add a new optimization pass working on Gimple. That pass would insert a Gimple statement (hopefully a call to some debugging print) before each Gimple call statement.
This is a non-trivial work (perhaps weeks of work). You need to understand all of Gimple