我正在使用c ++创建一个mysql应用程序
我想制作一个能够获得所需行的代码
然后我取这一行的价值
我把它放在第一个数组中并遍历列，直到这一行结束
然后我得到下一行把它放在array2中
然后我把整个array1放在数组类型的向量中
我之所以这样做，是因为我将遍历下一行并将新行值放在相同的2个数组中，但我需要在向量中保留旧的选定行，这些行的大小会随时间增加。
我尝试了其中一种方法，我认为向量中有指针而不是数组的实际数据
当我尝试获取旧的矢量值时，我发现最近的一个
这是代码：
if(mysql_query(conn, "SELECT * FROM price_ttl limit 10"))
{
print_error (conn,"");
}
res = mysql_store_result(conn);
//this variables are used to store information from res meta data using these functions
totalrows = mysql_num_rows(res);
numfields = mysql_num_fields(res);
/*here we will take value of each column in each row as string
then we will put it in certain position in array of 2 arrays
this array reperesnt 1 row
each array is formed of "12-1"numfields-1 places */
const int maxrows_price_ttl = 2;
const int maxcolumns_price_ttl = 11;//the last cloumn for null value
char two_rows_values_eleven_fields_1strow[maxcolumns_price_ttl];
char two_rows_values_eleven_fields_2ndrow[maxcolumns_price_ttl];
//second we make the vector of multiple arrays for price_mtl table rows
//int maxrows_price_mtl_var ;
//const int maxcolumns_price_mtl = 11;
//we define vector "dynamic array" which is of the type array and call it variable_rows_values_eleven_fields_vector
//the array which represent the type of the vector is called single_row_values_eleven_fields_array
//char *single_row_values_eleven_fields_array;
//here we define the vector its type char* its name variable_rows_values_eleven_fields_vector
std::vector<std::string> variable_rows_values_eleven_fields_vector_string;
std::vector<char*>variable_rows_values_eleven_fields_vector_array;
//this is to make sure we are present in place where mysql_fetch_row will get the desired row "row1"
mysql_data_seek(res, 0);
int rownumber=1;
int columnnumber=0;
std::string row_string="";
//char *row_array[];
//now we want to loop through the result set
for (rownumberall=1; rownumberall < totalrows; rownumberall++)
{
row_string="";
//third we get the value of the current row from result set of current query
//row = mysql_fetch_row (res);//>>>>>>>>>>>>--1-->>>>>--3--
//std::cout <<*(&row )<<std::endl;
//fputc ('\n', stdout);
//printf("Press any key to continue . . . ");
//fputc ('\n', stdout);
//_getch();
for (rownumber=1; rownumber <= maxrows_price_ttl; rownumber++)
{
//third we get the value of the current row from result set of current query
row = mysql_fetch_row (res);//>>>>>>>>>>>>--1-->>>>>--3--
for (columnnumber=0; columnnumber < numfields; columnnumber++)
{
if (rownumber==2)
{
//here we put each coloumn value in its place in array of arrays"which is similar to structure of price table from which we r geting our rows"
//we use rownumber-1 because array 1st place is zero first row is 1 first column is 0
two_rows_values_eleven_fields_2ndrow[columnnumber]= *row[columnnumber] ; //array first elemnt is zero >>>>>>>>>>>>>>--2--a
//std::cout <<two_rows_values_eleven_fields[rownumber-1][columnnumber]<<std::endl;
//printf("Press any key to continue . hawww. . ");
//fputc ('\n', stdout);
//_getch();
}
//row_array[columnnumber]= row[columnnumber] ;
if (rownumber==1)
{
two_rows_values_eleven_fields_1strow[columnnumber]= *row[columnnumber] ;
std::cout <<row_string<<std::endl;
row_string=row_string+row[columnnumber]+"," ;
}
//row_string=row_string+two_rows_values_eleven_fields[0][columnnumber]+"," ;
//std::cout <<row_string<<std::endl;
//fputc ('\n', stdout);
//printf("Press any key to continue . . . ");
//fputc ('\n', stdout);
//_getch();
}
if (rownumber==1)//so that we enter single time in vector
{
row_string.erase(row_string.end()-1);
row_string="'"+row_string+"'" ;
variable_rows_values_eleven_fields_vector_string.push_back(row_string);//>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>--2--b
variable_rows_values_eleven_fields_vector_array.push_back(two_rows_values_eleven_fields_1strow);//>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>--2--b
// std::cout <<row_string<<std::endl;
// std::cout <<variable_rows_values_eleven_fields_vector_string.back()<<std::endl;
// std::cout <<variable_rows_values_eleven_fields_vector_array.back()<<std::endl;
// std::cout <<variable_rows_values_eleven_fields_vector_array.back()[0]<<std::endl;
// std::cout <<variable_rows_values_eleven_fields_vector_array.back()[1]<<std::endl;
// std::cout <<variable_rows_values_eleven_fields_vector_array.back()[2]<<std::endl;
// fputc ('\n', stdout);
// printf("Press any key to continue . . . ");
// fputc ('\n', stdout);
// _getch();
}
}
//compare their difference for having same sign
//first we need to convert from string to double
//first we make varibles
double price_ttl_pricediff_row_1_double=0;
double price_ttl_pricediff_row_2_double=0;
//here we make string variable for string value of price_ttl pricediff which is extruded from row1 column 6 row 2 column6
std::string str_price_ttl_pricediff_row_1="";
std::string str_price_ttl_pricediff_row_2="";
//this is char pointer required by function strtod to point to begining of string after end of double part of the string to be converted
char *strtodpend;
const char *str_to_char_pointer2;
//here we give variables of price_ttl pricediff its values
str_to_char_pointer2=&two_rows_values_eleven_fields_1strow[5];
price_ttl_pricediff_row_1_double = strtod(str_to_char_pointer2,&strtodpend);
str_to_char_pointer2=&two_rows_values_eleven_fields_2ndrow[5];
price_ttl_pricediff_row_2_double = strtod(str_to_char_pointer2,&strtodpend);
//here this is how to get the sign of each of the two values
//sign(price_ttl_pricediff_row_1_double);
//sign(price_ttl_pricediff_row_2_double);
//this is to show the values of pricediff of price_ttl for test
std::cout <<two_rows_values_eleven_fields_1strow[5]<<std::endl;
std::cout <<two_rows_values_eleven_fields_2ndrow[5]<<std::endl;
std::cout <<str_to_char_pointer2 <<std::endl;
std::cout <<price_ttl_pricediff_row_2_double <<std::endl;
std::cout <<sign(price_ttl_pricediff_row_1_double)<<std::endl;
std::cout <<sign(price_ttl_pricediff_row_2_double) <<std::endl;
std::cout <<price_ttl_pricediff_row_1_double <<std::endl;
std::cout <<price_ttl_pricediff_row_2_double <<std::endl;
//std::cout <<str_price_ttl_pricediff <<std::endl;
//std::cout <<str_price_ttl_timediff <<std::endl;
//std::cout <<insert_into <<std::endl;
//fputc ('\n', stdout);
printf("Press any key to continue . . . ");
fputc ('\n', stdout);
_getch();
//if signs are not the same
if (sign(price_ttl_pricediff_row_1_double)!=sign(price_ttl_pricediff_row_2_double))
{
printf("Press any key to continue . . . ");
fputc ('\n', stdout);
_getch();
//here we calculate values of the row of mtl table from contents of vector
//first we know contents of vector
int vector_size =variable_rows_values_eleven_fields_vector_array.size();//size represents number of rows of price_ttl which will form one row for price_mtl
//we get all information from first and last element in vector
char *first_vector_array_row=variable_rows_values_eleven_fields_vector_array[0];
char *last_vector_array_row=variable_rows_values_eleven_fields_vector_array[(vector_size-1)];
std::cout <<variable_rows_values_eleven_fields_vector_array[0] <<std::endl;
std::cout <<variable_rows_values_eleven_fields_vector_array[1] <<std::endl;
std::cout <<variable_rows_values_eleven_fields_vector_array[2] <<std::endl;
std::cout <<*variable_rows_values_eleven_fields_vector_array[(vector_size-1)] <<std::endl;
std::cout <<variable_rows_values_eleven_fields_vector_string.back()<<std::endl;
std::cout <<variable_rows_values_eleven_fields_vector_string.size()<<std::endl;
std::cout <<vector_size<<std::endl;
variable_rows_values_eleven_fields_vector_string.push_back(row_string);
std::cout <<variable_rows_values_eleven_fields_vector_array[0] [0]<<std::endl;
std::cout <<variable_rows_values_eleven_fields_vector_array[0] [1]<<std::endl;
std::cout <<variable_rows_values_eleven_fields_vector_array[0] [2]<<std::endl;
std::cout <<variable_rows_values_eleven_fields_vector_array[0] [3]<<std::endl;
std::cout <<vector_size <<std::endl;
std::cout <<variable_rows_values_eleven_fields_vector_array[(vector_size-1)][0] <<std::endl;
std::cout <<variable_rows_values_eleven_fields_vector_array[(vector_size-1)] [1]<<std::endl;
std::cout <<variable_rows_values_eleven_fields_vector_array[(vector_size-1)] [2]<<std::endl;
std::cout <<variable_rows_values_eleven_fields_vector_array[(vector_size-1)] [3]<<std::endl;
std::cout <<vector_size <<std::endl;
//fputc ('\n', stdout);
printf("Press any key to continue . . . ");
fputc ('\n', stdout);
_getch();
答案 0 :(得分：0)
简而言之，我想制作2d矢量，它通过vector [] []获取元素然后我想从vector使用vector [] []重新获取元素以获得单个elemnts或vector []以获取整行的数组 可能吗？？？ 现在我只是输入行作为字符串向量，然后使用字符串函数通过分隔符检索每个元素 如果有人有其他方式我等待