Qt static lib submodule build - c

Question

I want to automate building thirdparty libraries and include them in my Qt project.
The .pro file of my Qt project looks like this:
QT -= gui
CONFIG += c++11 console
CONFIG -= app_bundle
QMAKE_EXTRA_TARGETS += stalib
PRE_TARGETDEPS += stalib
stalib.commands = make ../thirdparty/stalib/Makefile
LIBS += -L$${PWD}/../thirdparty/stalib/lib -lStalib
INCLUDEPATH += $${PWD}/../thirdparty/stalib/src
# The following define makes your compiler emit warnings if you use
# any feature of Qt which as been marked deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS
# You can also make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000 # disables all the APIs deprecated before Qt 6.0.0
SOURCES += main.cpp
The Makefile of my thirdparty depedency submodule looks like this:
#-----------------------------------------------#
# Makefile for hello world #
#-----------------------------------------------#
# add preprocessor define
DEF_PARAMS = -DGREET=\"world\"
# Just to make sure
ifndef CROSS_COMPILE
$(error "cross-compilation environment not activated properly")
endif
# add debug symbols, DO NOT overwrite contents of FLAGS, append!
CFLAGS += -g $(DEF_PARAMS)
#Compilation only ignore warnings (ignore/-w, show all/-Wall).
CFLAGS += -c -w
SOURCEDIR=./src
LIBDIR=./lib
#-----------------------------------------------#
# Project Specific Settings #
#-----------------------------------------------#
# include directories relative to $SDKTARGETSYSROOT/usr/include (system HEADERS) or this Makefile (project headers).
INC_PARAMS = $(SOURCEDIR)
# project headers
HEADERS = $(SOURCEDIR)/math.h
# project sources
SOURCES = $(SOURCEDIR)/math.c
# Object files.
OBJECTS=$(SOURCES:%.c=%.c.o)
# Link libraries
# Libraries search directories relative to $SDKTARGETSYSROOT/usr/libs
# Library name without lib and .so e.g. libm.so -> -lm.
LINK_LIBS=
#Target name
TARGET_STATIC = $(LIBDIR)/libStalib.a
#-----------------------------------------------#
# Print Make Parameters #
#-----------------------------------------------#
print-%:
#echo "SOURCES=$(SOURCES)"
#echo "HEADERS=$(HEADERS)"
#echo "DEF_PARAMS=$(DEF_PARAMS)"
#echo "CFLAGS=$(CFLAGS)"
#echo "LDFLAGS=$(LDLAGS)"
#echo $* = $($*)
#-----------------------------------------------#
# Makefile Make Executable #
#-----------------------------------------------#
.SUFFIXES: .c
#Build rules begin.
all: $(TARGET_STATIC)
#Build rule for static library target.
$(TARGET_STATIC): $(OBJECTS)
$(AR) rc $# $(OBJECTS)
#Build rule for dynamic library target.
$(TARGET_SHARED): $(OBJECTS)
$(LD) $(LDFLAGS) $(OBJECTS) $(LINK_LIBS) -o $#
#Build rule for executeable target
$(TARGET): $(OBJECTS)
$(CC) $(LDFLAGS) $^ $(LINK_LIBS) -o $#
#Compilation rule for c files.
%.c.o: %.c $(HEADERS)
$(CC) $(CFLAGS) $(INC_PARAMS) $< -o $#
#Clean-up object files and target.
clean:
rm -f $(OBJECTS) $(TARGET) $(TARGET_STATIC) $(TARGET_SHARED)
However I get a linker error when building. It can not find the function defined in the math.h file:
#ifndef MATHH
#define MATHH
int addNums(int a, int b);
#endif
But the strange thing is that QtCreator is able to follow the reference to the header file.
For all of you who want to check the sources directly, or fiddle around with them:
https://github.com/faxe1008/myapp
https://github.com/faxe1008/stalib
Any help or suggestions on how to improve are appreciated.

Answer 1

If you want to build the library automatically, then you need to modify this line in your .pro:
stalib.commands = make -C../thirdparty/stalib CROSS_COMPILE=1
But that is not your question. You don't show your .cpp code, but I guess that you forgot to surround your #include like this:
extern "C" {
#include "math.h"
}
You can't include non system C headers in C++ sources without that. See: https://isocpp.org/wiki/faq/mixing-c-and-cpp