Determining C executable name

Question

When we are compiling a C program the output is stored in a.out. How can we redirect the compiled output to another file?

Answer 1

With the -o option.

gcc main.c -o myCoolExecutable.o

This is ok if your program consists of a single file. If you have more files I suggest using make: create a Makefile and then run the command make.

A Makefile is a file containing some rules for compilation. An example can be the following (# means the line is a comment):

CXX = gcc

#CXXFLAGS = -std=c++11
#INC_PATH = ...
#LIBS = ...

SOURCEDIR := yourSourceFolder
SOURCES := $(wildcard $(SOURCEDIR)/*.c)
OBJDIR=$(SOURCEDIR)/obj

OBJECTS := $(patsubst $(SOURCEDIR)/%.c,$(OBJDIR)/%.o, $(SOURCES))
DEPENDS := $(patsubst $(SOURCEDIR)/%.c,$(OBJDIR)/%.d, $(SOURCES))

# ADD MORE WARNINGS!
WARNING := -Wall -Wextra

# .PHONY means these rules get executed even if
# files of those names exist.
.PHONY: all clean

# The first rule is the default, ie. "make",
# "make all" and "make parking" mean the same
all: yourExecutableName

clean:
    $(RM) $(OBJECTS) $(DEPENDS) yourExecutableName

# Linking the executable from the object files
# $^   # "src.c src.h" (all prerequisites)
yourExecutableName: $(OBJECTS)
    $(CXX) $(WARNING) $^ -o $@
    #$(CXX) $(WARNING) $(CXXFLAGS) $(INC_PATH) $^ -o $@ $(LIBS)

-include $(DEPENDS)

$(OBJDIR):
    mkdir -p $(OBJDIR)

$(OBJDIR)/%.o: $(SOURCEDIR)/%.c Makefile | $(OBJDIR)
    $(CXX) $(WARNING) -MMD -MP -c $< -o $@

Shortly CXX variable defines your compiler (gcc, g++), with CXXFLAGS you can define flags for your compilation (i.e. -std=c++11). Then you can include and define custom (INC_PATH and LIBS: not set in the example). With SOURCEDIR you can specify your source code directory (where *.c files are).Then SOURCES is basically telling that the source files for the compilation are all the files having extension *.c.

The Makefile contains a set of rules whose structure is the following:

output: inputs
    commandToExecute

The rule to generate your executable file is

yourExecutableName: $(OBJECTS)
    $(CXX) $(WARNING) $^ -o $@

which is equivalent to gcc -Wall -Wextra $(OBJECTS) -o yourExecutableName.

$(OBJECTS) are the object file resulting from the compilation. When the above rule is executed, if they are not found make will continue scanning the file to find a rule to generate them. In this case the rule to generate these files is:

$(OBJDIR)/%.o: $(SOURCEDIR)/%.c Makefile | $(OBJDIR)
    $(CXX) $(WARNING) -MMD -MP -c $< -o $@

If further information is needed let me know.