I am working on a C project for Linux-environment (compiled with gcc). I am using two libraries:
SDL image (source is stored at the directory SDL_img).
SDL TTF (source is stored at the directory SDL_ttf).
My CFLAGS variable:
CFLAGS = -std=c99 -pedantic-errors -Wall -g -lm `sdl-config --cflags` -ISDL_img -ISDL_ttf
As you can see, I am including those two library-directories.
My gcc command include the following:
`sdl-config --libs` -lSDLmain -lSDL -lSDL_img -lSDL_ttf
Finally, in my project I have the following includes:
#include "SDL_ttf.h"
#include "SDL_image.h"
For some reason, I get errors of the type:
undefined reference to 'IMG_Load'
Why?
EDIT:
all: Chess.o Commons.o Console.o Controls.o Coords.o File.o GameState.o GUI.o Keyboard.o List.o Minimax.o Move.o Piece.o SettingsState.o Slots.o Square.o Str.o
gcc $^ -lm -std=c99 -pedantic-errors -g -o Chess `sdl-config --libs` -lSDLmain -lSDL -lSDL_img -lSDL_ttf
Just cd to those src/SDL_xxx dirs and do make to build those libraries and then set the correct -L and -I. It failed on linking so the -I is "good" but your path to your libraries is incorect
basically linker is now searching its paths to find libSDL_img and libSDL_ttf then it also searches /usr/lib/x86_64-linux-gnu and it still can not find it, that is why you are getting undefined referecne.
To fix this: first build those SDL_xxx and then search where are those libraries and pass somethig like this along with other to gcc:
-Lsrc/SDL_img/lib -lSDL_img -Lsrc/SDL_ttf/lib -lSDL_ttf
Related
I want to use the ta_lib functions in my C code and am trying to import the ta_lib functions. The header file gets imported correctly but i cannot get the linker to find the actual library.
I want to do the compiling process with MAKE and gcc.
Firstly I import the header
#include <ta-lib/ta_libc.h>
And then when i need to use a function
TA_ADOSC(0, CSV_LENGTH - 1, temp_high, temp_low, temp_close, temp_volume, 3, 10, &beginIdx, &endIdx, tmp_adosc);
The program compiles fine using my makefile
# create CC variable
CC = gcc
# create CFLAGS variable
CFLAGS = -L/usr/local/lib -Wall -g
LDLIBS = -lta_lib -I/usr/local/include -lm
output: main.o
$(CC) $(CFLAGS) -o output main.o
main.o: main.c
$(CC) $(LDLIBS) -c main.c
# target: dependencies
# action
clean:
rm -f \*.o output
Once I try to run make i get the following
gcc -L/usr/local/lib -Wall -g -o output main.o
/usr/bin/ld: main.o: in function `calculate_indicators': main.c:(.text+0x226): undefined reference to `TA_ADOSC'
collect2: error: ld returned 1 exit status
make: \*\*\* \[Makefile:10: output\] Error 1
From my understanding I need to fix the linking to the shared library.
The library is installed:
ldconfig -p | grep libta_lib.so
Returns the following
libta_lib.so.0 (libc6,x86-64) => /usr/local/lib/libta_lib.so.0
libta_lib.so.0 (libc6,x86-64) => /lib/libta_lib.so.0
libta_lib.so (libc6,x86-64) => /usr/local/lib/libta_lib.so
libta_lib.so (libc6,x86-64) => /lib/libta_lib.so
Since i am fairly new to C and using external libraries I can't find what seems to be the problem
You are adding the libraries to the compile line. They need to be added to the link line. And preprocessor options like -I are used by the compiler, and "where to find libraries" options like -L are used by the linker.
Also, libraries always must come at the end of the link line, after all the object files. And, the -L "where to search" option should come before the -l "what library to find" option.
Write your rules like this:
CFLAGS = -I/usr/local/include -Wall -g
LDFLAGS = -L/usr/local/lib
LDLIBS = -lta_lib -lm
output: main.o
$(CC) $(CFLAGS) $(LDFLAGS) -o output main.o $(LDLIBS)
main.o: main.c
$(CC) $(CFLAGS) -c main.c
However, it's better to just let make do the work for you; it knows how to correctly compile things (as long as you set the standard variables). You don't need to include a rule to build main.o at all.
I have an SDL2 program that I've been developing on Ubuntu that I'd like to compile for windows. Right now I compile and run it with a makefile like this:
OBJECTS = main.o text.o object.o vector.o physics.o shapes.o target.o
run: all
./a.out
all: $(OBJECTS)
gcc $(OBJECTS) `sdl2-config --cflags --libs` -lSDL2_ttf -lSDL2_image -lm -ldl
main.o: main.c defs.h
gcc -c main.c `sdl2-config --cflags --libds` -lSDL2_ttf
text.o: text.c text.h defs.h
gcc -c text.c
object.o: object.c object.h defs.h
gcc -c object.c
vector.o: vector.c vector.h defs.h
gcc -c vector.c
physics.o: physics.c physics.h defs.h
gcc -c physics.c
shapes.o: shapes.c shapes.h defs.h
gcc -c shapes.c
target.o: target.c target.h defs.h
gcc -c target.c
clean:
rm *.o
I'd suggest quasi-msys2 cross-compilation environment (I'm the author).
From the first glance, your makefile should work in it with minimal changes:
sdl2-config doesn't work there (which is a minor defect), but pkg-config does.
Replace sdl2-config with pkg-config sdl2 SDL2_image SDL2_ttf (followed by --libs and/or --cflags).
Then -lSDL2_ttf -lSDL2_image should be removed, since pkg-config is going to output those anyway.
Note that pkg-config ... --libs should be used when linking, and pkg-config --cflags should be used when compiling (same with sdl2-config).
-ldl should be removed. -lm is unnecessary, but should be harmless.
gcc should be replaced with $CC to pick up the compiler from the environment variable.
While this doesn't affect correctness, manually specifying .h dependencies in makefiles is error-prone and tedious. Instead you should be compiling with -MMD -MP flags, to automatically generate the dependencies.
Since removing the dependencies makes all your .o recipes look very similar, you can deduplicate them into a single recipe:
%.o : %.c
$CC -c $< -MMD -MP
-MMD -MP is going to produce .d files (tiny makefile pieces), which need to be included using -include $(OBJECTS:.o=.d).
With those fixes, the makefile should work in quasi-msys2, except that the resulting executable is going to be called a.exe and not a.out...
# We're going to cross-compile with Clang. Install Clang, LLD, Wine. Then...
# Clone the repo
https://github.com/HolyBlackCat/quasi-msys2
cd quasi-msys2
# Install the necessary packages
make install _gcc _SDL2 _SDL2_image _SDL2_ttf
# Open the cross-compilation shell
# Among other things, this sets `CC` to a wrapper for Clang that invokes it
# with the right flags, and sets env variables for `pkg-config` to find the
# newly installed libs.
env/shell.sh
Then just run make as usual.
Whenever I run the following, I get undefined references to all the SDL-related functions used in my program:
cc -lSDL2 -lGL *.o
I believe this is caused by the lack of -l linker flags.
GCC arguments are positional, put the link flags after your o files:
gcc *.o -lSDL2 -lGL
Also, if you're on a proper full Linux system I'd recommend using pkg-config to pull compiler/linker flags:
gcc -c main.c `pkg-config sdl2 --cflags`
gcc main.o `pkg-config sdl2 --libs`
I am new to Makefile, C and Linux. I am using gcc & ubuntu. I encountered a problem while trying to compile the code with a link to a library.
Here is my problem. I have:
a_tests.c & b_tests.c files in "tests" folder
lib.a file in "build" folder
Here is the codes in Makefile related to the problem:
CFLAGS=-g -O2 -Wall -Wextra -Isrc -DNDEBUG $(OPTFLAGS)
TARGET=build/lib.a
TEST_SRC=$(wildcard tests/*_tests.c)
TESTS=$(patsubst %.c,%,$(TEST_SRC))
tests: CFLAGS += $(TARGET)
tests: $(TESTS)
When the tests files are compiled, "undefined reference to 'XXXfunction'"errors will be prompted. Because what executed behind is
gcc -g -O2 -Wall -Wextra -Isrc -DNDEBUG build/lib.a tests/a_tests.c -o test/a_tests
gcc -g -O2 -Wall -Wextra -Isrc -DNDEBUG build/lib.a tests/b_tests.c -o test/b_tests
But "build/lib.a" should be placed after the output file name to solve it (If I manually type in the below commands, the codes would be successfully compiled), ie:
gcc -g -O2 -Wall -Wextra -Isrc -DNDEBUG tests/a_tests.c -o test/a_tests build/lib.a
gcc -g -O2 -Wall -Wextra -Isrc -DNDEBUG tests/b_tests.c -o test/b_tests build/lib.a
But I don't know how to change in the Makefile, I tried -l -L options, they didn't work. It would warn that "cannot find the .a file". Any help would be appreciated. Thank you so much in advance!
Define the library as a dependency, because it is one. It will be appended at the end of the other dependencies, here: the source.
CFLAGS=-g -O2 -Wall -Wextra -Isrc -DNDEBUG $(OPTFLAGS)
TARGET=build/lib.a
TEST_SRC=$(wildcard tests/*_tests.c)
TESTS=$(TEST_SRC:%.c=%)
tests: $(TESTS)
$(TESTS): $(TARGET)
The library does not need to be after the output file, but after the depending input file.
The makefile is further simplified:
Replaced the patsubst with a simpler expression.
Moved the target tests up, so it is found as the first and therefore default target.
Good luck!
I have built OpenSSL from source (an intentionally old version; built with ./config && make && make test) and would prefer to use what I have built without doing make install to link against my program.
The command that's failing is:
gcc -Wall -Wextra -Werror -static -Lopenssl/openssl-0.9.8k/ -lssl -lcrypto
-Iopenssl/openssl-0.9.8k/include -o myApp source1.o source2.o common.o`
And I receive a series of errors similar to:
common.c:(.text+0x1ea): undefined reference to `SSL_write'
This makes me think there's something funky with my OpenSSL. If I omit -Lopenssl/openssl-0.9.8k/ from my command, the error changes to being unable to:
/usr/bin/ld: cannot find -lssl
/usr/bin/ld: cannot find -lcrypto
Am I compiling OpenSSL incorrectly? Or how should I best resolve this?
Silly "Linux-isms" strike again! Apparently, I need to change my command such that the -L and -l stuff is at the end like (despite what man gcc seems to indicate):
gcc -Wall -Wextra -Werror -static -o myApp source1.o source2.o common.o -Lopenssl/openssl-0.9.8k/ -lssl -lcrypto -Iopenssl/openssl-0.9.8k/include
Why don't you want to use make install? It can copy generated binaries in the directory you want if you previously passed it to ./configure --prefix $HOME/target_library_install_directory
If you used this trick with every library you build and install, you could then add the target directory to the LIBRARY_PATH environment variable and avoid using -L option.
If you use Autotools, or you are building an Autools project like cURL, then you should be able to use pkg-config. The idea is the Autotools package will read OpenSSL's package configuration and things will "just work" for you.
The OpenSSL package configuration library name is openssl.
You would use it like so in a makefile based project.
%.o: %.c
$(CC) -o $# -c `pkg-config --cflags openssl` $^
target: foo.o bar.o baz.o
$(CC) -o $# `pkg-config --libs openssl` $^
Also see How to use pkg-config in Make and How to use pkg-config to link a library statically.
Another approach is to use pkg-config to preserve compatibility. This is an example of makefile when needs to link OpenSSL.
CC = gcc
CFLAGS = \
-I. \
-D_GNU_SOURCE=1
LDFLAGS = `pkg-config --libs inih`
LDFLAGS += `pkg-config --libs libcurl`
LDFLAGS += `pkg-config --libs liburiparser`
LDFLAGS += `pkg-config --libs openssl`
# Executable
foo: foo.o
$(CC) -o $# $^ $(LDFLAGS)
foo.o: foo.c
$(CC) -c $(CFLAGS) $< -o $#