i've written a class from that i want to create a shared library. But this class uses other libraries. The call that i use to generate the library is of the form
g++ -fpic -c [necessary *.cpp files] [necessary includes]
Unfortunately this call leads to an error, namely iostream.h: No such file or directory.
But when i build a testfile using the library code it compiles and works properly.
Where might be the problem?
Thanks for your help.
Firstly, I'm pretty sure that you should be using iostream rather than iostream.h so you could try changing that in your source code. E.g.
#include <iostream>
Secondly, you need to check the include directives on the compilation line, as what you're getting is a compilation error indicating that the preprocessor can't find this file. As you haven't listed either your failed or successful commands here, I can't add much more than that.
Related
I'm doing the "Hello World" in the GTKMM tutorial, the "app" uses three files, the main.cc, helloworld.h and helloworld.cc.
At the beginning I thought that compiling the main.cc :
g++ -o HW main.cc $(pkg-config ... )
would be enough, but gives an error (undefined reference to Helloworld::Helloworld), etc.
In other words, it compiles the main and the header, but not the HW class, and this makes sense because the header is included in Main but not the Helloworld.cc. The thing is I'm kinda scared of including it because I read in other question that "including everything was a bad practice".
That being said, when I compile using all the files in the same command:
g++ -o HW main.cc helloworld.cc $(pkg-config ... )
the "app" works without errors.
So, since using the last command works, is compiling in this way a good practice?
What happens if my app uses a big ton of classes?
Must I manually write them all down in the command?
If not, must I use #include?
Is it good practice using #include for all cc used files?
Is normal to list all the cpp/cc files when compiling with g++?
Yes, completely.
How else will it know what source code you want it to compile?
The thing is I'm kinda scared of including it because I read in other question that including everything was a bad practice.
#includeing excess headers is bad practice.
Passing your complete source code to the compiler is not.
Is it good practice using #include for all cc used files?
Absolutely not.
What happens if my app uses a big ton of classes? Must I manually write them all down in the command?
No. You should be using a build system that handles this for you. That could be an IDE which takes all the files in your project and passes them to the compiler in turn, or it could be a CMakeLists.txt/Makefile with a *.cpp wildcard in (although I actually recommend listing source files explicitly, one-by-one; it's not hard).
Invoking g++ manually on the command-line is fine for a quick test, but for real usage you don't want to be clowning around with such machinery.
is good practice using #include for all cc used files
It's not only bad practice, never do it.
In order to create an executable you actually have to do two things:
Compile all the source code files to object files or libraries.
Link all the object files and needed libraries into an executable.
You seem to be missing the point that the link phase is where symbols defined in separate source files are resolved or linked.
Must I manually write them all down in the command?
For the compiler to know about the DEFINTION of the symbols DECLARED in your headers, you must include all source files. Exceptions to this rule can be (but are not limited to) headers containing template metaprogramming (TMP) code that usually exist entirely in header files.
What happens if my app uses a big ton of classes?
Most of the large C++ projects utilize build configuration tools such as CMAKE to handle the generation of makefiles for them.
I am unable to compile a C project that uses a library called "FFmpeg" with a compiler called "GCC", and I believe it might be either because I don't quite understand how #include works or because I am using the wrong compilation process.
In a folder called Test, I have a file Test/test.c with the following contents:
#include <stdio.h>
#include <stdlib.h>
#include "FFmpeg/libavcodec/avcodec.h"
The folder FFmpeg is located at Test/FFmpeg. When I try to compile this with GCC, I receive the following error:
fatal error: libavutil/samplefmt.h: No such file or directory
The file Test/FFmpeg/libavcodec/avcodec.h has the following code in it:
#include "libavutil/samplefmt.h"
#include "libavutil/attributes.h"
#include "libavutil/avutil.h"
... //many more #include statements
Is the issue here that I need to add "FFmpeg/" to all of these include statements?
If so, is there a way to automatically do this? This library is enormous and probably has hundreds of these statements.
If not, what should I be doing instead? Should I attempt to compile the library by itself? If so, how do I then include this compiled version of the library in my program?
Notes:
The command I am using to compile is gcc -c test.c.
I have GCC installed via MinGW.
I ultimately need to be able to compile this program to both a .dll and an .so.
I apologize if any of the terminology I use here is incorrect or if my explanations are poor. I know almost nothing about compilation. Please let me know if I need to fill in more information.
When #include is used with quotation marks (e.g. #include "file path here"), it will read that file path as a relative file path.
In the case of compiling a C program using GCC, file paths are relative to the current directory. The "current directory" is the one into which you have placed your command prompt using the cd command.
In my case, I cd'd into C:/Users/User/Documents/Test, meaning that all relative file paths are relative to C:/Users/User/Documents/Test. So when my compiler read
#include "libavutil/samplefmt.h"
it basically tried to do this:
#include C:/Users/User/Documents/Test/libavutil/samplefmt.h
when I instead needed the compiler to look at …/Test/FFmpeg/libavutil/samplefmt.h.
It turns out that the solution to this is to give the compiler additional locations to which relative paths might be relative. This is done with the -I[file path here] argument when you compile.
In my case, the way I needed to use this idea was to add C:/Users/User/Documents/Test/FFmpeg as a location to which paths might be relative. Thus, I could have taken my compile command:
gcc -c test.c
And inserted this:
gcc -IC:\Users\User\Documents\Test\FFmpeg -c test.c
However, this is actually an extremely clunky solution. There is a much easier way: it turns out that these file paths you provide with the -I argument can be relative to your current directory themselves. In my case, because my current directory in the command prompt was alreadyC:/Users/User/Documents/Test, I could simply remove this portion from the above command, shortening it to this:
gcc -IFFmpeg -c test.c
And this solved my problem.
I am using gcov for the first time to analyze my program (C++)
The program consists of three classes and I have built the project using Code::Blocks.
When I am invoking the program using the following command:
C:\Users\XXX\Documents\Test\TreeObjModel\src>gcc
-fprofile-arcs -ftest-coverage Tree.cpp
I receive the following error:
Tree.cpp:1:18: fatal error: Tree.h: No such file or directory
compilation terminated
While the cpp files are in the directory "C:\Users\XXX\Documents\Test\TreeObjModel\src\" , the header files are in directory "C:\Users\XXX\Documents\Test\TreeObjModel\include\"
Do we need to have both the code and header files in the same directory?
Thanks in advance.
You should use the -I flag to specify where your header files are.
Judging from your example, you should add -I../include
You have at least two options to instruct the compiler where to find the header files (includes).
-Ipath_to_includes as parameter for gcc compiler. E.g. -I../include
When including in your program, specify the directory. E.g. #include "../include/foo.h"
My strategy would be to just compile my project successfully and only then try to use some other stuff, like flags for code coverage. I say this because your error does not have anything to do with gcov, and trying to instrument your program to get code coverage before your program even compiles, makes things more complicated for you. One step at a time ;)
I'm trying to use libjson within a C++ project and the docs tell me to just "add libjson's source to your project, comment JSON_LIBRARY in the JSONOptions.h file and any C++ compiler should compile it."
Being quite new to C++ and all that, how exactly am I supposed to do that (not using any IDE)? Should I just #include the libjson.h file and that's it? Shouldn't I reference libjson somehow in my call to g++ when compiling my project?
thx in advance
If you go into the libjson library folder, you will see a makefile. Navigate to that directory in a terminal and type:
make
then
make install
Then, in your code
#include <libjson.h>
or, depending on your include path:
#include <libjson/libjson.h>
That should be all that you need to do.
If you need additional help, you can post in the help forum at sourceforge (I am the author of libjson)
You have to:
One,
#include <libjson.h>
in order to get access to the functions and data types the library offers, then
Two, link against the libjsonz library:
g++ -o myprogram myprogram.c -ljson
(the -ljson flag has to come last or you'll get a linker error with never versions of GCC.)
EDIT: if you need to build the library, you typically have a configure script or a Makefile. See how to use them.
if you install json you should find include file at /usr/local/include
so
#include <json/json.h>
gcc exasmple.c -ljson
I'm a new-ish C++ programmer, and I'm doing my first program on my own using C++. I decided I would like to use JSON to store some of the data I'm going to be using, and I've found a library to handle JSON, JsonCpp.
I've installed the library using my Linux system's package manager, and in my C++ code, I've used in my source code file
#include <json>
and compiled it using g++ and it's -ljson and -L/usr/lib options (libjson.so is located in /usr/lib).
However, the first usage of Json::Value, an object provided by the library, gives a compilation error of "Json has not declared". I'm sure my mistake is something simple, so could someone explain what I'm doing wrong? None of the books I had mention how to use shared libraries, so I've had to google to find this much.
EDIT: g++ with the -E option gives this error:
json: no such file or directory.
I checked the file list of JsonCPP:
include/json/autolink.h [code]
include/json/config.h [code]
include/json/features.h [code]
include/json/forwards.h [code]
include/json/json.h [code]
include/json/reader.h [code]
include/json/value.h [code]
include/json/writer.h [code]
Try #include <json/json.h> if the headers are installed in /usr/include. If they're installed somewhere else, mention this path with -I
g++ -I/my/lib/include -L/my/lib/lib -lmylib mysource.cpp
Did you also tell g++ where to find the header files via -I - this would be my guess at the problem.
That error pretty nearly certainly implies that you do not have the #include in the actual source file that gets the error.
use
g++ -E [whatever other options]
to see the cpp output would be one way to check and see what you've actually included.
It might help if you actually paste the error message; your comment suggests an error on the #include, but your question suggests something else.