C Makefile 链接错误：未定义对“主”的引用

Question

I have tried looking through other answers, unfortunately I have not found anyone with quite the same problem. I am trying to link two C files together, one has a header file, and the other the main file. When trying to make I receive this error:

(.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status

Below is the makefile I use to compile.

INC_DIR = include
SRC_DIR = src
BIN_DIR = bin
UNAME := $(shell uname)
CC = gcc
CFLAGS = -Wall -std=c11 -g -I$(INC_DIR) -I/usr/include/libxml2/
LDFLAGS= -L.

all: XMLParser

XMLParser: $(BIN_DIR)/XMLParser.o $(BIN_DIR)/SVGParser.o
    $(CC) $(CFLAGS) -o XMLParser $(BIN_DIR)/XMLParser.o $(BIN_DIR)/SVGParser.o

$(BIN_DIR)/XMLParser.o: $(SRC_DIR)/XMLParser.c $(INC_DIR)/SVGParser.h
    $(CC) $(CFLAGS) -o $(BIN_DIR)/XMLParser.o -c $(SRC_DIR)/XMLParser.c

$(BIN_DIR)/SVGParser.o: $(SRC_DIR)/SVGParser.c $(INC_DIR)/SVGParser.h
    $(CC) $(CFLAGS) `xml2-config --cflags --libs` -o $(BIN_DIR)/SVGParser.o $(SRC_DIR)/SVGParser.c

clean:
    rm *.o XMLParser $(BIN_DIR)/*

XMLParser.c has my main function:

int main(int argc, char **argv) {
  ...;
  return 0;
}

Answer 1

Your recipe for generating the intermediate SVGParser.o is attempting to link and generate a runnable executable. You need to add -c to skip the link step.

You will also need to remove the —libs on that object file and move it to the final link step. In other words add xml2-config —libs for the rule generating the final XMLParser target.

Disclaimer: I've never specifically used xml2-config , so I guess there's some chance I'm wrong here, but it's a very common paradigm for building and linking against complex libraries, I assume it's following the same patterns.

Answer 2

A full sample code showing the error must be posted to be able to test it elsewhere, so I cannot fully test your makefile, but providing a true main() and see what happens.

After generating stub files to check your Makefile I found the following output from make :

$ make
gcc -Wall -std=c11 -g -Iinclude -I/usr/include/libxml2/ -o bin/XMLParser.o -c src/XMLParser.c
gcc -Wall -std=c11 -g -Iinclude -I/usr/include/libxml2/ `xml2-config --cflags --libs` -o bin/SVGParser.o src/SVGParser.c
/usr/local/bin/ld: /usr/lib/gcc/x86_64-unknown-freebsd13.0/10.2.1/../../../crt1.o: en la función `_start':
/home/usr/src/lib/csu/amd64/crt1_c.c:75: referencia a `main' sin definir
collect2: error: ld devolvió el estado de salida 1
*** Error code 1

Stop.
make: stopped in /home/lcu/so/makefile
$ _

which is trying to link (alone) the module SVGParser.o (THIS IS BECAUSE YOU DIDN'T ADD THE -c COMPILATION OPTION TO COMPILE ONLY).

Change the compilation line for the SVGParser.o module to use the -c compile-only option and you will get the executable properly.