Section 5.3.7.2.3. Input to a C application program

When a DDL dictionary dictfile has been edited in accordance with the description above, the program BuildSiv may be run under a Unix-like operating system with a command of the form

BuildSiv dictfile ddlversion

where ddlversion takes the values `1' or `2' to indicate that a DDL1 or DDL2 parser is appropriate. If the option `-e' is given before dictfile, variable definitions and read capability for standard uncertainty values will be included as well. The name of the variable that will hold the standard uncertainty is the name given by the programmer with the string esd appended.

An object file cifsiv.o is produced together with a header file cifvars.h. Some source-code files are also produced as intermediate files in the lexical analysis and parse phases of the software build; these may be deleted. The object file must be linked against the other object files when the application program is compiled and references to the header files must be introduced (generally through C preprocessor #include directives) within the application code where access to the imported data structures is required.

Fig. 5.3.7.5 is an example of the header file cifvars.h built when BuildSiv reads the augmented dictionary of Fig. 5.3.7.4 with the `-e' option to interpret and store standard uncertainties.

Figure 5.3.7.5 | top | pdf | Header file cifvars.h for a C application built by BuildSiv from the augmented DDL dictionary of Fig. 5.3.7.4.

The integer variable errornum stores a nonzero value if an error occurs in attempting to read a CIF, and an error message is stored in the character array errormes, indicating the nature of the problem. Errors generated by the input subroutine cifsiv_ are not fatal to the parent application program, and will at worst discard the particular loop block or data item affected. The parser operates by discarding CIF data upon encountering an error until it reaches an understandable set of input values. So, for example, if three numbers appear after an item name instead of one, the second two will be ignored after the error variables have been set, and parsing will continue. Similarly, if a serious error occurs within a loop, such as the appearance of an item name not matching an array variable, the entire loop is normally ignored. If a new packet of looped data exceeds the specified array limits, all further data in that loop are ignored.

The cifsiv_ function has prototype

void cifsiv_ (char* filename , char* blockname )

and requires pointers to character strings containing the name of the input file and the data-block code from which input is required.

A simple example C application illustrating the use of the cifsiv_ subroutine is given in Fig. 5.3.7.6.

Figure 5.3.7.6 | top | pdf | An example C program designed to read CIF data as tagged in the augmented DDL dictionary of Fig. 5.3.7.4.