C动态链接库

[nonocast]

创建so

read.h

#ifndef READ_H
#define READ_H

int read();

#endif

read.c

#include "read.h"

int read() { return 123; }

Makefile

CC = gcc

build: read.o
	$(CC) -shared -o libReader330.so read.o

read.o: read.c
	$(CC) -c -o read.o read.c

.PHONY: build

$ make
gcc -c -o read.o read.c
gcc -shared -o libReader330.so read.o

然后就得到了so, 将此lib link到path中，

$ ln -s /.../.../libReader330.so /usr/local/lib

验证so

另起一个目录，

app.c

#include <stdio.h>

int read();

int main(void) {
  int ret = read();
  printf("ret: %d\n", ret);
  return 0;
}

Makefile

CC = gcc

build: 
	$(CC) -o app -lReader330 app.c

.PHONY: build

非常方便易懂:

$ make 
gcc -o app -lReader330 app.c
$ ./app
ret: 123

仔细考虑内存分配问题

read.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

unsigned char *SHGBIT_330_read(unsigned char **result) {
  char *message = "hello world, 330";
  int len = strlen(message);
  *result = (unsigned char *)malloc(len + 1);
  strcpy((char *)*result, message);
  *result[len] = 0x00;
  return *result;
}

app.c

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>

unsigned char *SHGBIT_330_read(unsigned char **result);

int main(void) {
  unsigned char *result;
  printf("%s\n", SHGBIT_330_read(&result));
  free(result);
  return 0;
}

so负责分配(malloc)内存，调用方负责释放(free)内存。