c ++ mysql查询字符串解析引号和变量(c++ mysql query string parsing with quotes and variables)

 我试图在不使用c ++中的mysql连接器类的情况下更新mysql数据库。 但我无法弄清楚如何将长整数添加到查询将接受的字符串。 
 
#define CONVERSION  16
    long myCounter   = 0 ;
    long gallons = 0;
    gallons = myCounter / CONVERSION;

    string sql = ("UPDATE utilityroom.Sprinklers SET "
        "gallons='@gallons' WHERE label='PUMP';");

    query_state = mysql_query(connection, sql);
    result = mysql_store_result(connection);            
 
 它一直在查询中的第二个参数失败。 
 
 错误：无法将'std :: string {aka std :: basic_string}'转换为'const char *'以将参数'2'转换为'int mysql_query（MYSQL *，const char *）' 
 
 编辑： 
 
 我讨厌c ++处理字符串的方式。 我不明白为什么每个字符串都必须转换为类元素！ 
 
 以下是我改变它以使其工作： 
 
    #include <sstream>
    ostringstream strstr;
    strstr << "UPDATE utilityroom.Sprinklers SET gallons='" << gallons << "' WHERE label='PUMP';";
    string sql = strstr.str();
    query_state = mysql_query(connection, sql.c_str());

I am trying to update a mysql database without using mysql connector class in c++. But I can't figure out how to add a long integer to a string that the query will accept.
 
#define CONVERSION  16
    long myCounter   = 0 ;
    long gallons = 0;
    gallons = myCounter / CONVERSION;

    string sql = ("UPDATE utilityroom.Sprinklers SET "
        "gallons='@gallons' WHERE label='PUMP';");

    query_state = mysql_query(connection, sql);
    result = mysql_store_result(connection);            
 
It keeps failing at the 2nd argument in the query.
 
error: cannot convert ‘std::string {aka std::basic_string}’ to ‘const char*’ for argument ‘2’ to ‘int mysql_query(MYSQL*, const char*)’
 
EDIT:
 
I hate the way c++ handles strings. I don't understand why every string has to be converted to a class element!
 
Here is what I changed to get it working:
 
    #include <sstream>
    ostringstream strstr;
    strstr << "UPDATE utilityroom.Sprinklers SET gallons='" << gallons << "' WHERE label='PUMP';";
    string sql = strstr.str();
    query_state = mysql_query(connection, sql.c_str());

原文：https://stackoverflow.com/questions/41666357