gcc won't compile SDL C Program (undefined reference to SDL functions)

Question

I recently moved to linux and i\'m having an issue with compiling SDL C programs using gcc.

The command i\'m using:

gcc `sdl-config --cflags --libs`          


        

Answer 1

Order of arguments to gcc matters a lot.

Read about Invoking GCC (and documentation of binutils, which gcc uses). Then replace

 gcc `sdl-config --libs` -o main main.o

with

 gcc main.o  `sdl-config --libs` -o main

Better yet, learn how to use GNU make (it is often using GNU bash) and use a Makefile inspired by this answer...

Also, always pass -Wall -g to gcc until your program is bug-free (then use -Wall -O2)

Take inspiration from open source programs on github or gitlab using SDL. Consider also using other open source libraries and frameworks, such as Qt, SFML, GTKmm, etc... And study their example code.

Answer 2

Add -lSDL with gcc compile command. This will add sdl library. Install sdl developement package before compiling.

EDIT:

gcc -o out main.c -lSDL

or

gcc -I/usr/include/SDL/ main.c -o out -L/usr/lib -lSDL

Answer 3

Thanks a lot for the advices ! This helped me to solve an old mystery about SDL symbols never found under Linux :-) As wroten in the comments, the order of gcc line is essential. The makefile was not well written and this was causing the breakage you mentionned.

As summary, use : gcc ( flags ) -o name ( include et linking options)

Last but not least, under x86_64, use gdb64, instead of gdb ( was the next headhache ;-)

As example, a little Makefile I wrote myself (ok, not that good, but works)

# Makefile pour le contrôle du robot Arduino 
# Controle Robot
# Sauf mention contraire, tout est place sous Licence GPL V2
# Historique : 
# Etienne HAMON / création du makefile initial (d'après cours IFT1), Novembre 2014
#
# Corrections du Makefile : Eric Bachard décembre 2014 

CC = gcc
C_STANDARD = -std=c99
INCLUDE_DIR = inc -I/usr/include/SDL
SOURCES_DIR = sources
BUILD_DIR = build
APPLICATION_NAME = Controle
FILENAME = ${BUILD_DIR}/${APPLICATION_NAME}
CFLAGS = -Wall -ansi ${C_STANDARD}
LDFLAGS = -lSDL $(sdl-config --static-libs) -lm
DEBUG_SUFFIX = _debug
CFLAGS_DEBUG = -v -gdwarf-2 -DDEBUG
OBJS = ${SOURCES_DIR}/*.c

all : ${FILENAME} ${FILENAME}${DEBUG_SUFFIX}

${FILENAME}: ${OBJS}
    ${CC} ${CFLAGS} -o $@  $^ -I${INCLUDE_DIR} ${LDFLAGS} 

${FILENAME}${DEBUG_SUFFIX}: ${OBJS}
    ${CC} ${CFLAGS} ${CFLAGS_DEBUG} -o $@ $^ -I${INCLUDE_DIR} ${LDFLAGS} 

clean:
    ${RM} *.o ${FILENAME} ${FILENAME}${DEBUG_SUFFIX}
    ${RM} -rf ${BUILD_DIR}/*.dSYM

Answer 4

None of the "popular" answers for this question are correct or working. Some of them have nothing to even do with the question being asked. I have the same problem.

SDL docs give an example for compiling like this: gcc -o main main.c `sdl2-config --cflags --libs`

Yet user is suggesting that it is order of arguments causing the problem!! It is not! In fact, their suggested order is something I have never seen before and is certainly not any kind of standard. SDL answers on this site are very low quality!

Update: I found a solution for some missing functions. SDL_SetVideoMode does not exist in SDL2. Use SDL_CreateWindow.

Answer 5

I See this from /usr/include/SDL2/SDL_main.h

/* * This is called by the real SDL main function to let the rest of the * library know that initialization was done properly. * * Calling this yourself without knowing what you're doing can cause * crashes and hard to diagnose problems with your application. */ extern DECLSPEC void SDL_SetMainReady(void);

Also check this: nm /usr/lib/i386-linux-gnu/libSDL.a | grep SDL_SetMainReady

This is not the solution but will allow you to focus on the real problem, I think it is not the compilation process.