#define函数

本是古典何须时尚 2022-06-09 01:07 76阅读 0赞

一直以为\#define只能宏定义简单变量和简单函数，虽然也知道宏定义编译过程中就是替换，但是今天才真正明白替换的意义：请看如下代码：  
关键：define PARAM\_WRITE(x,y) param\_vendor\_write(x,y)

#include<stdio.h>
    #define PARAM_CONFIG "/home/lkg/test/config" //配置文件路径
    #define VENDOR_WRITE 0
    #ifdef VENDOR_WRITE
        #define PARAM_WRITE(x,y) param_vendor_write(x,y)
    #else
        #define PARAM_WRITE(x,y) param_write_cfg(x,y)
    #endif
    typedef struct{
        unsigned short int id;
        int offset;
    }param_offset;     //根据id查找偏移进行参数设置
    typedef struct {
        char c;
        int h;
        unsigned short n;
        char s[4];
    }st;  //测试用例结构体
    param_offset id_offset[3] =  {
        {
       1,0},
        {
       2,8},                    
        {
       3,108},                  
    };//设置不同id写文件的偏移量用于后续查询
    /*
     *根据id在文件的指定偏移处写数据
     */
    int param_vendor_write(st* buffer, unsigned short int param_id){
        printf("param vendor write");
    }
    int param_write_cfg(st* buffer, unsigned short int param_id){
        int ret, i, offset;
        FILE *fp;
        i = 0;
        while(id_offset && id_offset[i].id){
            if(param_id == id_offset[i].id){
                offset = id_offset[i].offset;
                break;
            }
            i++;
        }//根据id查找对于偏移量
        printf("id = %d, offset = %d\n", param_id, offset);    
        if((fp = fopen(PARAM_CONFIG, "rb+")) == NULL) {
            if((fp = fopen(PARAM_CONFIG, "wb+")) == NULL) {
                printf("Can't open %s, program will to exit.\n", PARAM_CONFIG);
                return -1;
            }
        }
        fseek(fp, offset, SEEK_SET);
        fwrite(buffer, sizeof(*buffer), 1, fp);
        printf("st c = %d, h = %d n =%u s = %s \n",buffer->c, buffer->h,buffer->n,buffer->s); 
        fclose(fp);
        return 0;
    }
    /*
     *
     *读取文件指定id位置存储的结构体内容
     *
     */
    int param_read_cfg(st* buffer, unsigned short int param_id){
        int ret, i, offset;
        FILE *fp;
        param_offset id_offset[3] =  {
            {
       1,0},
            {
       2,8},                    
            {
       3,108},                  
        }; 
        i = 0;
        while(id_offset && id_offset[i].id){
            if(param_id == id_offset[i].id){
                offset = id_offset[i].offset;
                break;
            }
            i++;
        }  
        printf("id = %d, offset = %d\n", param_id, offset);        
        if((fp = fopen(PARAM_CONFIG, "rb+")) == NULL) {
            printf("Can't open %s, program will to exit.", PARAM_CONFIG);
            return -1;
        }  
        fseek(fp, offset, SEEK_SET);
        fread(buffer, sizeof(*buffer), 1, fp);
        printf("st c = %d, h = %d n =%u s = %s \n",buffer->c, buffer->h,buffer->n,buffer->s);
        fclose(fp);
        return 0; 
    
    }
    int main(){
    //    char version[] = "1.0.5";
        st t;
        st tt = {
       5,7,0,"didi"};
        st tt1 = {
       6,2,0,"dada"};
    //    param_write_cfg(version,1);
        PARAM_WRITE(&tt,2);
        PARAM_WRITE(&tt1,3);
        param_read_cfg(&t,2);
        param_read_cfg(&t,3);
        return 0;
    }