Question

I’m coding a C++ application that needs to interact with a postgres DB.
I would like to initialize the table datas using a COPY statement.

Here’s the code :

EXEC SQL BEGIN DECLARE SECTION ;
  const char * fileData_name = file_data_name ;
EXEC SQL END DECLARE SECTION ;

EXEC SQL COPY datas
         FROM :fileData_name
         WITH (FORMAT text, DELIMITER '|') ;

Here’s the error message from ecpg :

ERROR: syntax error at or near ":fileData_name"

According to the postgres documentation :
This style of inserting C variables in SQL statements works anywhere a value expression is expected in an SQL statement.

If COPY stuff FROM field, then my guess is that field is not a value expression.

Any help ?

thx 🙂

Answer 1

Well, it’s not possible to do that… according to this post. But it’s possible to use prepared statements :

char * sql_template = 
    "COPY datas FROM '%s' WITH (FORMAT text, DELIMITER '|');" ;
const char * file_name = "myfile.data";
unsigned int sql_command_len = 
    strlen (sql_template) - 2 + strlen (file_name) + 1;

EXEC SQL BEGIN DECLARE SECTION ; 
    char * sql_command = (char*) malloc (sizeof(char)*sql_command_len) ; 
EXEC SQL END DECLARE SECTION ; 

sprintf (sql_command, sql_template, file_name) ;

EXEC SQL PREPARE cpy FROM :sql_command;
EXEC SQL EXECUTE cpy ;
EXEC SQL DEALLOCATE PREPARE cpy ;
free (sql_command) ;