C语言可以通过调用Oracle函数来实现数据库操作。Oracle函数可以实现对数据的查询、更新、插入等操作。如下是一个C语言调用Oracle函数的示例：

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<oci.h>
int main(int argc, char **argv)
{
// 定义需要连接的数据库信息
char *db_conn_str = "hostname:port/service_name";
char *user = "username";
char *pwd = "password";
// 初始化OCI环境
OCIEnv *envhp;
OCIInitialize((ub4) OCI_DEFAULT, (dvoid *)0, (dvoid * (*)(dvoid *, size_t)) 0, (dvoid * (*)(dvoid *, dvoid *, size_t)) 0,  (void (*)(dvoid *, dvoid *)) 0 );
OCIEnvCreate(&envhp, OCI_THREADED|OCI_OBJECT, (dvoid *)0, (dvoid * (*)(dvoid *, size_t)) 0, (dvoid * (*)(dvoid *, dvoid *, size_t)) 0,  (void (*)(dvoid *, dvoid *)) 0, (size_t) 0, (dvoid **)0);
// 创建OCI会话
OCISvcCtx *svchp;
OCIHandleAlloc((dvoid *)envhp, (dvoid **)&svchp, OCI_HTYPE_SVCCTX, 0, (dvoid **) 0 );
// 创建OCI错误句柄
OCIError *errorhp;
OCIHandleAlloc((dvoid *)envhp, (dvoid **)&errorhp, OCI_HTYPE_ERROR, 0, (dvoid **) 0 );
// 连接数据库
OCISession *authp;
OCIAttrSet((dvoid *)svchp, OCI_HTYPE_SVCCTX, (dvoid *)user, strlen(user), OCI_ATTR_USERNAME, errorhp);
OCIAttrSet((dvoid *)svchp, OCI_HTYPE_SVCCTX, (dvoid *)pwd, strlen(pwd), OCI_ATTR_PASSWORD, errorhp);
OCILogon2(svchp, errorhp, &authp, (OraText *) db_conn_str, strlen(db_conn_str), (OraText *) user, strlen(user), (OraText *) pwd, strlen(pwd), OCI_DEFAULT);
// 创建OCI执行句柄
OCIStmt *stmthp;
OCIHandleAlloc((dvoid *)envhp, (dvoid **)&stmthp, OCI_HTYPE_STMT, 0, (dvoid **) 0 );
// 执行Oracle函数
OCIBind *bndhp;
int input_val = 1;
OCIParam *paramhp;
int output_val;
ub4 output_val_len;
char *function_name = "test_function";
OCIStmtPrepare(stmthp, errorhp, (OraText *)function_name, strlen(function_name), OCI_NTV_SYNTAX, OCI_DEFAULT);
OCIParamGet(stmthp, OCI_HTYPE_STMT, errorhp, &paramhp, 1);
OCIAttrSet(paramhp, OCI_HTYPE_DESC, (dvoid *)&output_val, sizeof(int), OCI_ATTR_DATA_TYPE, errorhp);
OCIAttrSet(paramhp, OCI_HTYPE_DESC, (dvoid *)&output_val_len, sizeof(ub4), OCI_ATTR_DATA_SIZE, errorhp);
OCIBindByPos(stmthp, &bndhp, errorhp, 1, (dvoid *)&input_val, sizeof(int), SQLT_INT, (dvoid *)0, (ub2 *)0, (ub2 *)0, 0, (ub4 *)0, OCI_DEFAULT);
OCIStmtExecute(svchp, stmthp, errorhp, 1, 0, 0, 0, OCI_DEFAULT);
// 打印结果
printf("Output Value: %d\n", output_val);
// 释放OCI资源
OCIHandleFree((dvoid *)bndhp, OCI_HTYPE_BIND);
OCIHandleFree((dvoid *)paramhp, OCI_HTYPE_DESCRIBE);
OCIHandleFree((dvoid *)stmthp, OCI_HTYPE_STMT);
OCILogoff(svchp, errorhp);
OCIHandleFree((dvoid *)authp, OCI_HTYPE_SESSION);
OCIHandleFree((dvoid *)errorhp, OCI_HTYPE_ERROR);
OCIHandleFree((dvoid *)svchp, OCI_HTYPE_SVCCTX);
OCIHandleFree((dvoid *)envhp, OCI_HTYPE_ENV);
return 0;
}

上述示例中，首先定义了需要连接的数据库信息，然后初始化OCI环境。接着创建OCI会话和OCI错误句柄，并通过OCILogon2函数连接数据库。然后创建OCI执行句柄，并调用OCIStmtPrepare和OCIParamGet函数设置Oracle函数的参数。最后通过OCIBindByPos和OCIStmtExecute函数执行Oracle函数，并通过OCIAttrGet函数获取函数的返回值。 总之，C语言调用Oracle函数是一项非常重要的技能，可用于实现各种数据库操作。通过使用示例代码，开发者可以更轻松地实现C语言调用Oracle函数。