C语言通过ODBC函数操作Access数据库（mdb和accdb格式）（char字符数组）-编程知识

编译环境：Windows XP + Visual Studio 2010
数据库：Access 2010，accdb格式
本例程只使用char[]字符数组，不使用wchar_t[]字符数组，更适合C语言初学者。
如果读取字符串时，提供的字符数组空间小了，db_fetch会执行失败返回-1。
由于Windows系统设计原因，char[]字符数组只能存储GB2312编码的字符串，wchar_t[]字符数组只能存储UTF-16编码的字符串。如果是UTF-8编码的字符串（也用char[]数组存储），必须用MultiByteToWideChar函数转成UTF-16格式（用wchar_t[]数组存储，CodePage参数=CP_UTF8），再调用W版本的API函数操作数据库。

请注意，Visual Studio里面使用以_s结尾的函数时，凡是参数名是maxcount的，都要减1，否则程序会闪退。
_snprintf_s函数的正确用法：
_snprintf_s(str, sizeof(str), sizeof(str) - 1, "fmt"); // C语言专用
_snprintf_s(str, sizeof(str) - 1, "fmt"); // C++专用, 和上面的语句等效

如果系统是32位，请编译并运行32位版本的程序；如果系统是64位，请编译并运行64位版本的程序，否则无法成功连接数据库。

主代码（main.c）：

#include <stdio.h>
#include "db.h"void show_products()
{char *sql;char name[50];double price;int id, num;size_t namelen;Statement stmt;sql = "SELECT [产品ID], [产品名称], [单价], [库存量] FROM [产品] WHERE [产品ID] <= 4 ORDER BY [产品ID]";stmt = db_query(sql);if (stmt != NULL){db_bind_int(stmt, 1, &id);db_bind_str(stmt, 2, name, sizeof(name), &namelen);db_bind_double(stmt, 3, &price);db_bind_int(stmt, 4, &num);while (db_fetch(stmt) == 1)printf("%d %s(len=%d) %.2lf %d\n", id, name, (int)namelen, price, num);db_free(stmt);}sql = "SELECT * FROM [产品] WHERE [产品名称] = '苏打水'";printf("exists: %d\n", db_has_records(sql));
}void find_product_by_id(int id)
{char *sql;char name[50];Statement stmt;sql = "SELECT [产品名称], [单价], [库存量] FROM [产品] WHERE [产品ID] = ?";stmt = db_prepare(sql);if (stmt != NULL){db_set_int(stmt, 1, &id);db_exec_stmt(stmt, 0);while (db_fetch(stmt) == 1){printf("find %d: %s %.2f %d\n", id, db_get_str(stmt, 1, name, sizeof(name), NULL), db_get_float(stmt, 2), db_get_int(stmt, 3));}db_free(stmt);}
}void find_product_by_name(const char *name)
{char *sql;Statement stmt;sql = "SELECT [产品ID], [单价], [库存量] FROM [产品] WHERE [产品名称] = ?";stmt = db_prepare(sql);if (stmt != NULL){db_set_str(stmt, 1, name);db_exec_stmt(stmt, 0);while (db_fetch(stmt) == 1)printf("find %s: %d %.2lf %d\n", name, db_get_int(stmt, 1), db_get_double(stmt, 2), db_get_int(stmt, 3));db_free(stmt);}
}void update_products()
{char *sql;double dval;int cnt;Statement stmt;sql = "UPDATE [产品] SET [库存量] = [库存量] + 1 WHERE [产品ID] = 1";db_exec(sql, &cnt);printf("update: cnt=%d\n", cnt);sql = "UPDATE [产品] SET [库存量] = [库存量] + 1 WHERE [产品名称] = ?";stmt = db_prepare(sql);if (stmt != NULL){db_set_str(stmt, 1, "牛奶");db_exec_stmt(stmt, 0);cnt = db_affected_rows(stmt);printf("update: cnt=%d\n", cnt);db_free(stmt);}sql = "UPDATE [产品] SET [单价] = [单价] + ? WHERE [产品名称] = ?";stmt = db_prepare(sql);if (stmt != NULL){dval = 0.25;db_set_double(stmt, 1, &dval);db_set_str(stmt, 2, "盐");db_exec_stmt(stmt, 0);cnt = db_affected_rows(stmt);printf("update: cnt=%d\n", cnt);db_free(stmt);}
}int main()
{int ret;ret = db_connect("test.accdb");if (ret == -1){printf("%s\n", db_geterror());return -1;}show_products();find_product_by_id(14);find_product_by_name("饼干");update_products();db_disconnect();return 0;
}

db.h：

#pragma oncetypedef void *Statement;/* 数据库连接与断开 */
int db_connect(const char *filename);
void db_disconnect();
const char *db_geterror();/* Prepared Statement 相关 */
Statement db_prepare(const char *sql);
int db_exec_stmt(Statement stmt, int free);
// 设置SQL语句中的问号
void db_set_int(Statement stmt, int i, const int *p);
void db_set_str(Statement stmt, int i, const char *s);
void db_set_float(Statement stmt, int i, const float *p);
void db_set_double(Statement stmt, int i, const double *p);/* 直接执行查询，不Prepare */
Statement db_query(const char *sql); // 执行SELECT查询，需要手动释放资源
int db_affected_rows(Statement stmt); // 获取INSERT、UPDATE和DELETE语句影响的行数
int db_exec(const char *sql, int *affected_cnt); // 执行普通查询
int db_has_records(const char *sql); // 直接执行SELECT查询，判断结果集是否有记录
void db_free(Statement stmt); // 释放db_query的资源/* 记录集操作 */
int db_fetch(Statement stmt); // 获取一行记录
// 绑定字段到变量上
void db_bind_int(Statement stmt, int col, int *p); // 以整数类型保存第col列的内容
void db_bind_str(Statement stmt, int col, char *buf, int len, size_t *real_len); // 以字符串类型保存第col列的内容
void db_bind_float(Statement stmt, int col, float *p); // 以小数类型保存第col列的内容
void db_bind_double(Statement stmt, int col, double *p);
// 直接读取字段内容
int db_get_int(Statement stmt, int col); // 直接以整数类型读取第col列的内容
char *db_get_str(Statement stmt, int col, char *buf, int len, size_t *real_len); // 直接以字符串类型读取第col列的内容
float db_get_float(Statement stmt, int col); // 直接以小数类型读取第col列的内容
double db_get_double(Statement stmt, int col);

db.c：

/* 
这个文件里封装了很多操作数据库的函数
参考资料：https://msdn.microsoft.com/en-us/library/ms714562%28v=vs.85%29.aspx
*/
#include <stdio.h>
#include <Windows.h>
#include <sqlext.h>
#include "db.h"#define DB_DSN "Driver={Microsoft Access Driver (*.mdb, *.accdb)};Dbq=%s;"static char db_errmsg[500];
static BOOL db_connected;
static SQLHENV db_env;
static SQLHDBC db_dbc;int db_connect(const char *filename)
{char fullpath[MAX_PATH] = ""; // 数据库文件完整路径char dsn[MAX_PATH + 100]; // 数据库连接字符串char code[6]; // 错误代码char msg[500]; // 错误信息char *p;SQLRETURN rc;rc = SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &db_env);if (!SQL_SUCCEEDED(rc))goto err;rc = SQLSetEnvAttr(db_env, SQL_ATTR_ODBC_VERSION, (SQLPOINTER)SQL_OV_ODBC3, 0);if (!SQL_SUCCEEDED(rc))goto err;rc = SQLAllocHandle(SQL_HANDLE_DBC, db_env, &db_dbc);if (!SQL_SUCCEEDED(rc))goto err;// 根据数据库文件名生成数据库连接字符串if (filename[1] != ':'){GetModuleFileNameA(NULL, fullpath, sizeof(fullpath));p = strrchr(fullpath, '\\');if (p != NULL)*(p + 1) = '\0';}strncat_s(fullpath, sizeof(fullpath), filename, sizeof(fullpath) - 1);_snprintf_s(dsn, sizeof(dsn), sizeof(dsn) - 1, DB_DSN, fullpath);// 根据连接字符串连接数据库rc = SQLDriverConnectA(db_dbc, NULL, dsn, SQL_NTS, NULL, 0, NULL, 0);if (!SQL_SUCCEEDED(rc)){// 获取连接失败的错误提示rc = SQLGetDiagRecA(SQL_HANDLE_DBC, db_dbc, 1, code, NULL, msg, sizeof(msg), NULL);goto err;}db_connected = TRUE;return 0; // 连接成功时，函数返回0err:db_disconnect();if (SQL_SUCCEEDED(rc))_snprintf_s(db_errmsg, sizeof(db_errmsg), sizeof(db_errmsg) - 1, "连接数据库失败。\n错误代码: %s\n错误信息: %s", code, msg);elsestrcpy_s(db_errmsg, sizeof(db_errmsg), "未知错误。");return -1; // 连接失败时，函数返回-1
}void db_disconnect()
{if (db_dbc != SQL_NULL_HDBC){if (db_connected){SQLDisconnect(db_dbc);db_connected = FALSE;}SQLFreeHandle(SQL_HANDLE_DBC, db_dbc);db_dbc = SQL_NULL_HDBC;}if (db_env != SQL_NULL_HENV){SQLFreeHandle(SQL_HANDLE_ENV, db_env);db_env = SQL_NULL_HENV;}
}const char *db_geterror()
{return db_errmsg;
}Statement db_prepare(const char *sql)
{SQLHSTMT stmt;SQLRETURN rc;rc = SQLAllocHandle(SQL_HANDLE_STMT, db_dbc, &stmt);if (!SQL_SUCCEEDED(rc))return NULL;SQLPrepareA(stmt, (char *)sql, (int)strlen(sql));return stmt;
}int db_exec_stmt(Statement stmt, int free)
{SQLRETURN rc;rc = SQLExecute(stmt);if (free)db_free(stmt);if (!SQL_SUCCEEDED(rc))return -1;return 0;
}void db_set_int(Statement stmt, int i, const int *p)
{static SQLLEN size = sizeof(int); // 该变量的地址必须固定, 所以要加staticSQLBindParameter(stmt, i, SQL_PARAM_INPUT, SQL_C_LONG, SQL_INTEGER, 0, 0, (int *)p, 0, &size); // 整型变量的地址也必须固定
}void db_set_str(Statement stmt, int i, const char *s)
{static SQLLEN len = SQL_NTS;SQLBindParameter(stmt, i, SQL_PARAM_INPUT, SQL_C_CHAR, SQL_VARCHAR, strlen(s), 0, (char *)s, 0, &len);
}void db_set_float(Statement stmt, int i, const float *p)
{static SQLLEN size = sizeof(float);SQLBindParameter(stmt, i, SQL_PARAM_INPUT, SQL_C_FLOAT, SQL_FLOAT, 0, 0, (float *)p, 0, &size);
}void db_set_double(Statement stmt, int i, const double *p)
{static SQLLEN size = sizeof(double);SQLBindParameter(stmt, i, SQL_PARAM_INPUT, SQL_C_DOUBLE, SQL_DOUBLE, 0, 0, (double *)p, 0, &size);
}Statement db_query(const char *sql)
{SQLRETURN rc;Statement stmt;stmt = db_prepare(sql);if (stmt == NULL)return NULL;rc = SQLExecute(stmt);if (!SQL_SUCCEEDED(rc)){db_free(stmt);return NULL;}return stmt;
}// 此函数只能用于获取INSERT、UPDATE和DELETE语句影响的行数
// 无法获取SELECT语句查询返回的记录集的行数
int db_affected_rows(Statement stmt)
{SQLLEN cnt;SQLRETURN rc;if (stmt == NULL)return -1;rc = SQLRowCount(stmt, &cnt);if (!SQL_SUCCEEDED(rc))return -1;return (int)cnt;
}int db_exec(const char *sql, int *affected_cnt)
{Statement stmt;stmt = db_query(sql);if (affected_cnt != NULL)*affected_cnt = db_affected_rows(stmt);if (stmt == NULL)return -1;db_free(stmt);return 0;
}int db_has_records(const char *sql)
{int ret;Statement stmt;stmt = db_query(sql);if (stmt == NULL)return 0;ret = db_fetch(stmt);db_free(stmt);return ret;
}void db_free(Statement stmt)
{SQLFreeHandle(SQL_HANDLE_STMT, stmt);
}int db_fetch(Statement stmt)
{SQLRETURN rc;rc = SQLFetch(stmt);if (rc == SQL_SUCCESS)return 1;else if (rc == SQL_NO_DATA)return 0;elsereturn -1;
}void db_bind_int(Statement stmt, int col, int *p)
{SQLBindCol(stmt, col, SQL_C_LONG, p, sizeof(int), NULL);
}void db_bind_str(Statement stmt, int col, char *buf, int len, size_t *real_len)
{SQLBindCol(stmt, col, SQL_C_CHAR, buf, len, real_len);
}void db_bind_float(Statement stmt, int col, float *p)
{SQLBindCol(stmt, col, SQL_C_FLOAT, p, sizeof(float), NULL);
}void db_bind_double(Statement stmt, int col, double *p)
{SQLBindCol(stmt, col, SQL_C_DOUBLE, p, sizeof(double), NULL);
}int db_get_int(Statement stmt, int col)
{int n;SQLRETURN ret;ret = SQLGetData(stmt, col, SQL_C_LONG, &n, sizeof(int), NULL);if (SUCCEEDED(ret))return n;elsereturn 0;
}char *db_get_str(Statement stmt, int col, char *buf, int len, size_t *real_len)
{SQLRETURN ret;ret = SQLGetData(stmt, col, SQL_C_CHAR, buf, len, real_len);if (!SUCCEEDED(ret)){buf[0] = '\0';if (real_len != NULL)*real_len = 0;}return buf;
}float db_get_float(Statement stmt, int col)
{float n;SQLRETURN ret;ret = SQLGetData(stmt, col, SQL_C_FLOAT, &n, sizeof(float), NULL);if (SUCCEEDED(ret))return n;elsereturn 0;
}double db_get_double(Statement stmt, int col)
{double n;SQLRETURN ret;ret = SQLGetData(stmt, col, SQL_C_DOUBLE, &n, sizeof(double), NULL);if (SUCCEEDED(ret))return n;elsereturn 0;
}