Receiving main.o error - c++

Question

The compiler in Qt Creator does not support c++11. So in my .pro file I added QMAKE_CXXFLAGS += -std=c++11
So my .pro file now looks like this:
TEMPLATE = app
QMAKE_CXXFLAGS += -std=c++11
CONFIG += console
CONFIG -= app_bundle
CONFIG -= qt
SOURCES += main.cpp \
server.cpp \
Section.cpp \
mainwindow.cpp \
main2.cpp \
client.cpp \
Chapter.cpp \
Book.cpp
HEADERS += \
Year.h \
Term.h \
Student.h \
Section.h \
mainwindow.h \
Load.h \
List.h \
Course.h \
ContentManager.h \
client.h \
Chapter.h \
Book.h
OTHER_FILES += \
Makefile \
D2.pro.user
This is my makefile:
#############################################################################
# Makefile for building: D2
# Generated by qmake (2.01a) (Qt 4.8.1) on: Mon Nov 10 23:00:21 2014
# Project: D2.pro
# Template: app
# Command: /usr/bin/qmake-qt4 -spec /usr/share/qt4/mkspecs/linux-g++ CONFIG+=debug CONFIG+=declarative_debug -o Makefile D2.pro
#############################################################################
####### Compiler, tools and options
CC = gcc
CXX = g++
DEFINES = -DQT_WEBKIT
CFLAGS = -pipe -g -Wall -W $(DEFINES)
CXXFLAGS = -pipe -std=c++11 -g -Wall -W $(DEFINES)
INCPATH = -I/usr/share/qt4/mkspecs/linux-g++ -I.
LINK = g++
LFLAGS =
LIBS = $(SUBLIBS)
AR = ar cqs
RANLIB =
QMAKE = /usr/bin/qmake-qt4
TAR = tar -cf
COMPRESS = gzip -9f
COPY = cp -f
SED = sed
COPY_FILE = $(COPY)
COPY_DIR = $(COPY) -r
STRIP = strip
INSTALL_FILE = install -m 644 -p
INSTALL_DIR = $(COPY_DIR)
INSTALL_PROGRAM = install -m 755 -p
DEL_FILE = rm -f
SYMLINK = ln -f -s
DEL_DIR = rmdir
MOVE = mv -f
CHK_DIR_EXISTS= test -d
MKDIR = mkdir -p
####### Output directory
OBJECTS_DIR = ./
####### Files
SOURCES = main.cpp \
server.cpp \
Section.cpp \
mainwindow.cpp \
main2.cpp \
client.cpp \
Chapter.cpp \
Book.cpp
OBJECTS = main.o \
server.o \
Section.o \
mainwindow.o \
main2.o \
client.o \
Chapter.o \
Book.o
DIST = /usr/share/qt4/mkspecs/common/unix.conf \
/usr/share/qt4/mkspecs/common/linux.conf \
/usr/share/qt4/mkspecs/common/gcc-base.conf \
/usr/share/qt4/mkspecs/common/gcc-base-unix.conf \
/usr/share/qt4/mkspecs/common/g++-base.conf \
/usr/share/qt4/mkspecs/common/g++-unix.conf \
/usr/share/qt4/mkspecs/qconfig.pri \
/usr/share/qt4/mkspecs/modules/qt_webkit_version.pri \
/usr/share/qt4/mkspecs/features/qt_functions.prf \
/usr/share/qt4/mkspecs/features/qt_config.prf \
/usr/share/qt4/mkspecs/features/exclusive_builds.prf \
/usr/share/qt4/mkspecs/features/default_pre.prf \
/usr/share/qt4/mkspecs/features/debug.prf \
/usr/share/qt4/mkspecs/features/default_post.prf \
/usr/share/qt4/mkspecs/features/declarative_debug.prf \
/usr/share/qt4/mkspecs/features/unix/gdb_dwarf_index.prf \
/usr/share/qt4/mkspecs/features/warn_on.prf \
/usr/share/qt4/mkspecs/features/resources.prf \
/usr/share/qt4/mkspecs/features/uic.prf \
/usr/share/qt4/mkspecs/features/yacc.prf \
/usr/share/qt4/mkspecs/features/lex.prf \
/usr/share/qt4/mkspecs/features/include_source_dir.prf \
D2.pro
QMAKE_TARGET = D2
DESTDIR =
TARGET = D2
first: all
####### Implicit rules
.SUFFIXES: .o .c .cpp .cc .cxx .C
.cpp.o:
$(CXX) -c $(CXXFLAGS) $(INCPATH) -o "$#" "$<"
.cc.o:
$(CXX) -c $(CXXFLAGS) $(INCPATH) -o "$#" "$<"
.cxx.o:
$(CXX) -c $(CXXFLAGS) $(INCPATH) -o "$#" "$<"
.C.o:
$(CXX) -c $(CXXFLAGS) $(INCPATH) -o "$#" "$<"
.c.o:
$(CC) -c $(CFLAGS) $(INCPATH) -o "$#" "$<"
####### Build rules
all: Makefile $(TARGET)
$(TARGET): $(OBJECTS)
$(LINK) $(LFLAGS) -o $(TARGET) $(OBJECTS) $(OBJCOMP) $(LIBS)
{ test -n "$(DESTDIR)" && DESTDIR="$(DESTDIR)" || DESTDIR=.; } && test $$(gdb --version | sed -e 's,[^0-9]\+\([0-9]\)\.\([0-9]\).*,\1\2,;q') -gt 72 && gdb --nx --batch --quiet -ex 'set confirm off' -ex "save gdb-index $$DESTDIR" -ex quit '$(TARGET)' && test -f $(TARGET).gdb-index && objcopy --add-section '.gdb_index=$(TARGET).gdb-index' --set-section-flags '.gdb_index=readonly' '$(TARGET)' '$(TARGET)' && rm -f $(TARGET).gdb-index || true
Makefile: D2.pro /usr/share/qt4/mkspecs/linux-g++/qmake.conf /usr/share/qt4/mkspecs/common/unix.conf \
/usr/share/qt4/mkspecs/common/linux.conf \
/usr/share/qt4/mkspecs/common/gcc-base.conf \
/usr/share/qt4/mkspecs/common/gcc-base-unix.conf \
/usr/share/qt4/mkspecs/common/g++-base.conf \
/usr/share/qt4/mkspecs/common/g++-unix.conf \
/usr/share/qt4/mkspecs/qconfig.pri \
/usr/share/qt4/mkspecs/modules/qt_webkit_version.pri \
/usr/share/qt4/mkspecs/features/qt_functions.prf \
/usr/share/qt4/mkspecs/features/qt_config.prf \
/usr/share/qt4/mkspecs/features/exclusive_builds.prf \
/usr/share/qt4/mkspecs/features/default_pre.prf \
/usr/share/qt4/mkspecs/features/debug.prf \
/usr/share/qt4/mkspecs/features/default_post.prf \
/usr/share/qt4/mkspecs/features/declarative_debug.prf \
/usr/share/qt4/mkspecs/features/unix/gdb_dwarf_index.prf \
/usr/share/qt4/mkspecs/features/warn_on.prf \
/usr/share/qt4/mkspecs/features/resources.prf \
/usr/share/qt4/mkspecs/features/uic.prf \
/usr/share/qt4/mkspecs/features/yacc.prf \
/usr/share/qt4/mkspecs/features/lex.prf \
/usr/share/qt4/mkspecs/features/include_source_dir.prf
$(QMAKE) -spec /usr/share/qt4/mkspecs/linux-g++ CONFIG+=debug CONFIG+=declarative_debug -o Makefile D2.pro
/usr/share/qt4/mkspecs/common/unix.conf:
/usr/share/qt4/mkspecs/common/linux.conf:
/usr/share/qt4/mkspecs/common/gcc-base.conf:
/usr/share/qt4/mkspecs/common/gcc-base-unix.conf:
/usr/share/qt4/mkspecs/common/g++-base.conf:
/usr/share/qt4/mkspecs/common/g++-unix.conf:
/usr/share/qt4/mkspecs/qconfig.pri:
/usr/share/qt4/mkspecs/modules/qt_webkit_version.pri:
/usr/share/qt4/mkspecs/features/qt_functions.prf:
/usr/share/qt4/mkspecs/features/qt_config.prf:
/usr/share/qt4/mkspecs/features/exclusive_builds.prf:
/usr/share/qt4/mkspecs/features/default_pre.prf:
/usr/share/qt4/mkspecs/features/debug.prf:
/usr/share/qt4/mkspecs/features/default_post.prf:
/usr/share/qt4/mkspecs/features/declarative_debug.prf:
/usr/share/qt4/mkspecs/features/unix/gdb_dwarf_index.prf:
/usr/share/qt4/mkspecs/features/warn_on.prf:
/usr/share/qt4/mkspecs/features/resources.prf:
/usr/share/qt4/mkspecs/features/uic.prf:
/usr/share/qt4/mkspecs/features/yacc.prf:
/usr/share/qt4/mkspecs/features/lex.prf:
/usr/share/qt4/mkspecs/features/include_source_dir.prf:
qmake: FORCE
#$(QMAKE) -spec /usr/share/qt4/mkspecs/linux-g++ CONFIG+=debug CONFIG+=declarative_debug -o Makefile D2.pro
dist:
#$(CHK_DIR_EXISTS) .tmp/D21.0.0 || $(MKDIR) .tmp/D21.0.0
$(COPY_FILE) --parents $(SOURCES) $(DIST) .tmp/D21.0.0/ && (cd `dirname .tmp/D21.0.0` && $(TAR) D21.0.0.tar D21.0.0 && $(COMPRESS) D21.0.0.tar) && $(MOVE) `dirname .tmp/D21.0.0`/D21.0.0.tar.gz . && $(DEL_FILE) -r .tmp/D21.0.0
clean:compiler_clean
-$(DEL_FILE) $(OBJECTS)
-$(DEL_FILE) *~ core *.core
####### Sub-libraries
distclean: clean
-$(DEL_FILE) $(TARGET)
-$(DEL_FILE) Makefile
check: first
compiler_rcc_make_all:
compiler_rcc_clean:
compiler_uic_make_all:
compiler_uic_clean:
compiler_image_collection_make_all: qmake_image_collection.cpp
compiler_image_collection_clean:
-$(DEL_FILE) qmake_image_collection.cpp
compiler_yacc_decl_make_all:
compiler_yacc_decl_clean:
compiler_yacc_impl_make_all:
compiler_yacc_impl_clean:
compiler_lex_make_all:
compiler_lex_clean:
compiler_clean:
####### Compile
main.o: main.cpp Course.h \
Year.h \
Term.h \
Student.h \
ContentManager.h \
Book.h \
List.h \
Chapter.h \
Section.h \
Load.h
$(CXX) -c $(CXXFLAGS) $(INCPATH) -o main.o main.cpp
server.o: server.cpp
$(CXX) -c $(CXXFLAGS) $(INCPATH) -o server.o server.cpp
Section.o: Section.cpp Section.h
$(CXX) -c $(CXXFLAGS) $(INCPATH) -o Section.o Section.cpp
mainwindow.o: mainwindow.cpp mainwindow.h \
client.h
$(CXX) -c $(CXXFLAGS) $(INCPATH) -o mainwindow.o mainwindow.cpp
main2.o: main2.cpp mainwindow.h \
client.h
$(CXX) -c $(CXXFLAGS) $(INCPATH) -o main2.o main2.cpp
client.o: client.cpp client.h
$(CXX) -c $(CXXFLAGS) $(INCPATH) -o client.o client.cpp
Chapter.o: Chapter.cpp Chapter.h \
List.h \
Section.h
$(CXX) -c $(CXXFLAGS) $(INCPATH) -o Chapter.o Chapter.cpp
Book.o: Book.cpp Book.h \
List.h \
Chapter.h \
Section.h
$(CXX) -c $(CXXFLAGS) $(INCPATH) -o Book.o Book.cpp
####### Install
install: FORCE
uninstall: FORCE
FORCE:
Unfortunately, I'm getting this error: [main.o] Error 1
This error was non-existent before adding c++11. I can't solve this problem. Can someone please help me here?
UPDATE:
Typing in gcc -v in the command line in Qt creator gave me:
Starting command 'gcc -v'
Using built-in specs.
COLLECT_GCC=/usr/bin/gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/i686-linux-gnu/4.6/lto-wrapper
Target: i686-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.6.3-1ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.6 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --enable-objc-gc --enable-targets=all --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=i686-linux-gnu --host=i686-linux-gnu --target=i686-linux-gnu
Thread model: posix
gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5)
'gcc -v' finished
I think the compiler version is 4.6.3, which means it supports C++11

Answer 1

There's more to that error message than just [main.o] Error 1. Paste the whole error message.
However, some guesses as to your problem might include:
You use both $(OBJCOMP) and $(SUBLIBS) in your linker command, but neither of them is defined anywhere. Could this be the cause of the error?
Some old versions of g++ (for example, 4.6.3) spell the option -std=c++0x instead of -std=c++11. Depending on the output of g++ --version, you might need to use the older spelling.
You might need to add -std=c++11 to the LFLAGS as well as to the CXXFLAGS, to make sure that you're linking against the correct C++ library. (I don't know of any systems for which this matters, but I always try to get it right anyway.)

Answer 2

I got this error a few times as well.
I was frankly amazed at the lack of information in the error message, well, I mean, there is basically none.
Here is my interpretation of what the erro means:
main.o doesn't exist / can't be found / is entirely broken.
There are a few ways you could've ended up in this situation:
Location where main.o is supposed to be written is write protected. (You could try toggling shadowbuild in Qt creator)
You're out of space (I know, sounds absurd with 8TB HDDs on the market. This was what was happening for me tho.)
Your project is ill configured. (Sometimes there is a difference between / and \ in paths)
Your compiler is ill configured.
There is something very wrong with your code.

Answer 3

Unfortunately, I'm getting this error: [main.o] Error 1
.....
Believe me, that was the only error. I tried all your suggestions but none could solve the problem, unfortunately
Interestingly, Qt Creator does not remove your project's Makefile even if you do Cleaning and Rebuilding.
Those options does remove your output binary files (including .o files), but sometimes it can't be sufficient especially when you're editing the .pro file or .qrc file.
In most cases where the build error message is unclear and it's claimed, "Well it just worked before!" it's worth trying making sure that you're building it completely from the scratch all the way through by:
Going to your build directory such as:
../build-*
Deleting all relevant Makefile scripts and others if necessary,
Then re-building it again.