我创建了一个MySQL表，其中一列存储BLOB类型。 （互联网告诉我BLOB是图像的正确数据类型。）
我几乎都是C ++和MySQL的初学者。我想要做的是编写一个带有main（）的小程序，将jpeg放入该表中。为了本练习，我不想存储对包含图像的目录的引用。
我认为这就像在下面的BLOCK 2中填写部分一样简单吗？
#include <iostream>
#include <string>
#include <mysql.h>
using namespace std;
int main(int argc, char **argv)
{
//BLOCK 1: INIT
MYSQL *connection, mysql;
MYSQL_RES *result;
MYSQL_ROW row;
int query_state;
mysql_init(&mysql);
connection = mysql_real_connect(&mysql, "localhost", "root", "secret", "beginner_db",0,0,0);
//BLOCK 2: SEND QUERY
/* do something to insert image to table */
//BLOCK 3: DISPLAY QUERY RESULTS
result = mysql_store_result(connection);
/* do something with result */
//BLOCK 4: FREE
mysql_free_result(result);
mysql_close(connection);
return 0;
}
答案 0 :(得分：1)
我发现这个解决方案适用于10kb以下的图像。
//http://zetcode.com/tutorials/mysqlcapitutorial/
//g++ -o output source.cpp $(mysql_config --cflags) $(mysql_config --libs)
#include <stdio.h>
#include <iostream>
#include <mysql.h>
int main(int argc, char **argv)
{
MYSQL *conn;
int len, size;
char data[1000*1024];
char chunk[2*1000*1024+1];
char query[1024*5000];
FILE *fp;
conn = mysql_init(NULL);
mysql_real_connect(conn, "localhost", "root", "secret", "beginner_db", 0, NULL, 0);
fp = fopen("filename.png", "rb");
size = fread(data, 1, 1024*1000, fp);
mysql_real_escape_string(conn, chunk, data, size);
char *stat = "INSERT INTO pic_tbl(name, pic) VALUES('cexample', '%s')";
len = snprintf(query, sizeof(stat)+sizeof(chunk) , stat, chunk);
mysql_real_query(conn, query, len);
fclose(fp);
mysql_close(conn);
}
答案 1 :(得分：1)
对于这种情况，一个好的解决方案是使用mysql_stmt_send_long_data()函数。
我链接到的MySQL手册页上有一个例子，但这里是一个更相关的发送文件内容的例子：
#ifdef _WIN32
#include <windows.h>
#endif
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <boost/scope_exit.hpp>
#include <mysql.h>
#define ARR_LEN(arr_id) ((sizeof (arr_id))/(sizeof (arr_id)[0]))
int main()
{
using namespace std;
MYSQL *pconn = mysql_init(NULL);
BOOST_SCOPE_EXIT( (pconn) ) {
mysql_close(pconn);
} BOOST_SCOPE_EXIT_END
const char *db_name = "test";
if (!mysql_real_connect(pconn, "localhost", "test", "********", db_name, 0, NULL, CLIENT_COMPRESS)) {
cerr << "Error: mysql_real_connect() failed to connect to `" << db_name << "`." << endl;
return EXIT_FAILURE;
}
MYSQL_STMT *pinsert_into_images_stmt = mysql_stmt_init(pconn);
BOOST_SCOPE_EXIT( (pinsert_into_images_stmt) ) {
mysql_stmt_close(pinsert_into_images_stmt);
} BOOST_SCOPE_EXIT_END
const char sql1[] = "INSERT INTO images(data) VALUES (?)";
if (mysql_stmt_prepare(pinsert_into_images_stmt, sql1, strlen(sql1)) != 0) {
cerr << "Error: mysql_stmt_prepare() failed to prepare `" << sql1 << "`." << endl;
return EXIT_FAILURE;
}
MYSQL_BIND bind_structs[] = {
{ 0 } // One for each ?-placeholder
};
unsigned long length0;
bind_structs[0].length = &length0;
bind_structs[0].buffer_type = MYSQL_TYPE_BLOB;
bind_structs[0].is_null_value = 0;
if (mysql_stmt_bind_param(pinsert_into_images_stmt, bind_structs) != 0) {
cerr << "Error: mysql_stmt_bind_param() failed." << endl;
return EXIT_FAILURE;
}
const char *file_name = "image.jpg";
FILE *fp = fopen(file_name, "rb");
BOOST_SCOPE_EXIT( (fp) ) {
fclose(fp);
} BOOST_SCOPE_EXIT_END
// Use mysql_stmt_send_long_data() to send the file data in chunks.
char buf[10*1024];
while (!ferror(fp) && !feof(fp)) {
size_t res = fread(buf, 1, ARR_LEN(buf), fp);
if (mysql_stmt_send_long_data(pinsert_into_images_stmt, 0, buf, res) != 0) {
cerr << "Error: mysql_stmt_send_long_data() failed." << endl;
return EXIT_FAILURE;
}
}
if (!feof(fp)) {
cerr << "Error: Failed to read `" << file_name << "` in its entirety." << endl;
return EXIT_FAILURE;
}
if (mysql_stmt_execute(pinsert_into_images_stmt) != 0) {
cerr << "Error: mysql_stmt_execute() failed." << endl;
return EXIT_FAILURE;
}
cout << "Inserted record #" << mysql_insert_id(pconn) << endl;
return EXIT_SUCCESS;
}
我使用表`images`的以下定义：
CREATE TABLE images (
id INT UNSIGNED NOT NULL AUTO_INCREMENT,
data MEDIUMBLOB NOT NULL,
PRIMARY KEY (id)
);
运行此程序后，它成功将38,339字节的JPEG image.jpg发送到服务器并输出“已插入的记录＃1”。
您可以验证是否发送了正确的字节数：
mysql> SELECT octet_length(data) FROM images WHERE id=1; +--------------------+ | octet_length(data) | +--------------------+ | 38339 | +--------------------+ 1 row in set (0.00 sec)
答案 2 :(得分：0)
这样的事情：
CString SaveFile( CMemoryFile& File )
{
*pFileKey = -1;
SQLRETURN retcode;
SQLHSTMT hstmt;
CLoggEntryList LoggEntryList( this ); // logg entries cannot be made while busy inside the hstmt, use this class to add them later
SQLINTEGER cbDocumentBlock; // For binding the main image
long lDocumentBufferSize = 0;
unsigned char* pDocumentBuffer; // Will be set to point to the buffer that should be written into the document blob field
unsigned char pDummyChar[] = {'0'}; // Dummy buffer to write in the image/thumbnail blob fields when using external storage
lDocumentBufferSize = File.m_lBufferSize;
pDocumentBuffer = File.m_pFileBuffer;
// Allocate statement handle
retcode = SQLAllocHandle(SQL_HANDLE_STMT, m_Database.m_hdbc, &hstmt);
if (retcode == SQL_SUCCESS || retcode == SQL_SUCCESS_WITH_INFO)
{ // Create a result set
CString szSQL;
szSQL = ( "INSERT INTO ObjectTable (ObjectData) VALUES ( ? )");
retcode = SQLPrepare(hstmt, (SQLCHAR*)szSQL.GetBuffer(), SQL_NTS);
if (retcode == SQL_SUCCESS || retcode == SQL_SUCCESS_WITH_INFO)
{
// Bind the parameters. For parameter 1, pass the parameter number in ParameterValuePtr instead of a buffer address.
SQLINTEGER cbNULL = 0;
SQLINTEGER cbTEXT = SQL_NTS;
int nColumn = 1;
// Bind ObjectData
cbDocumentBlock = SQL_LEN_DATA_AT_EXEC(0); //SQL_LEN_DATA_AT_EXEC(lImageBufferSize);
retcode = SQLBindParameter(hstmt, nColumn++, SQL_PARAM_INPUT, SQL_C_BINARY, SQL_LONGVARBINARY,
0, 0, (SQLPOINTER) DOCUMENT, 0, &cbDocumentBlock);
if (retcode == SQL_SUCCESS || retcode == SQL_SUCCESS_WITH_INFO)
{
// Set values so data for parameter 1 will be passed at execution. Note that the length parameter in
// the macro SQL_LEN_DATA_AT_EXEC is 0. This assumes that the driver returns "N" for the
// SQL_NEED_LONG_DATA_LEN information type in SQLGetInfo.
retcode = SQLExecute(hstmt);
const long nMaxChunkSize = 400000;
// For data-at-execution parameters, call SQLParamData to get the parameter number set by SQLBindParameter.
// Call InitUserData. Call GetUserData and SQLPutData repeatedly to get and put all data for the parameter.
// Call SQLParamData to finish processing this parameter.
while (retcode == SQL_NEED_DATA)
{
SQLPOINTER pToken;
retcode = SQLParamData(hstmt, &pToken);
switch( (int)pToken )
{
case DOCUMENT:
{
if (retcode == SQL_NEED_DATA)
{
for( int nPos = 0; nPos < lDocumentBufferSize; nPos += nMaxChunkSize )
{
int nBufferSize = min( lDocumentBufferSize - nPos, nMaxChunkSize );
SQLRETURN retcode2 = SQLPutData(hstmt, pDocumentBuffer+nPos, nBufferSize );
if (retcode2 != SQL_SUCCESS && retcode2 != SQL_SUCCESS_WITH_INFO)
{
SQLCHAR Sqlstate[6];
SQLINTEGER NativeError;
SQLCHAR MessageText[201];
SQLSMALLINT TextLengthPtr;
retcode2 = SQLGetDiagRec( SQL_HANDLE_STMT, hstmt, 1, Sqlstate, &NativeError, MessageText, 200, &TextLengthPtr );
if (retcode2 == SQL_SUCCESS || retcode2 == SQL_SUCCESS_WITH_INFO)
{
MessageText[TextLengthPtr] = 0;
Sqlstate[5] = 0;
CString szSQLState( Sqlstate );
CString szMessageText( MessageText );
CString szMessage;
szMessage.Format("Error in SaveFile(). SQL State %s. Native %ld. Source: %s", szSQLState, NativeError, szMessageText );
SQLFreeHandle(SQL_HANDLE_STMT, hstmt);
return szMessage;
}
}
}
}
break;
}
default:
{
CString szMessage;
szMessage.Format("Error in SaveBuffer(). Unknown parameter buffer.");
SQLFreeHandle(SQL_HANDLE_STMT, hstmt);
return szMessage;
}
break;
}
}
}
SQLRETURN retcode3;
retcode3 = SQLFreeHandle(SQL_HANDLE_STMT, hstmt);
ASSERT(retcode3 == SQL_SUCCESS);
}
}
}
此代码未经过测试，甚至未经过编译，但它应该指向正确的方向。