C++ 获取mysql数据库以blob类型储存的图片

最近遇到个用C++代码取出以blob类型存放在mysql数据库里面图片的需求, 粗略的翻了翻mysql的api文档, 写了个最简单的实现:

#include <iostream>
#include <fstream>
#include <sstream>
#include <cstring>
#include <mysql/mysql.h>
using namespace std;

int main()
{
    const char username[] = "username";
    const char password[] = "password";
    const char host[]   = "192.168.0.100";
    const char dbname[] = "dbname";

    MYSQL conn;
    if(mysql_init(&conn) == nullptr) {
        cerr << "init conn fail." << endl;
        exit(-1);
    }

    if (mysql_real_connect(&conn, host, username, password, dbname, 0, NULL, 0) == nullptr) {
        cerr << "connect to database error" << endl;
        exit(-1);
    }

    char sql[] = "select octet_length(picture), picture from tablename";
    if (mysql_real_query(&conn, sql, strlen(sql)) != 0) {
        cerr << "query error." << endl;
        exit(-1);
    }

    MYSQL_RES * result = NULL;
    result = mysql_store_result(&conn);
    if (result == nullptr) {
        cerr << "store result error." << endl;
        exit(-1);
    }

    if (mysql_affected_rows(&conn) <= 0) {
        cerr << "no data be found." << endl;
        exit(-1);
    }

    int count = 0;
    string path = "/home/sakuragl/pictures/";
    MYSQL_ROW row_record;
    while (row_record = mysql_fetch_row(result)) {
        unsigned int size = 0;
        char * temp_buff = NULL;

        sscanf(row_record[0], "%d", &size);
        if(size == 0) {
            cerr << "invalid record!" << endl;
            continue;
        }

        temp_buff = (char *)malloc(size * sizeof(char) + 1);
        if(temp_buff == nullptr) {
            cerr << "malloc error!" <<endl;
            exit(1);
        }
        memset(temp_buff, 0, size * sizeof(char) + 1);
        memcpy(temp_buff, row_record[1], size * sizeof(char));

        stringstream pic_name;
        pic_name << count << ".jpg";
        ofstream outfile(path + pic_name.str(), ios::binary);
        outfile.write(temp_buff, size);

        count++;
        free(temp_buff);
    }

    mysql_close(&conn);
    return 0;
}