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HOME > Monitoring_and_Data > Oceanic and Atmospheric Data > Reanalysis: Atmospheric Data >
wgrib2
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wgrib2: a sample function
Introduction
Wgrib2 is "function" driven. Options on the command line corresponds to a function call.
When wgrib2 is started, each option-function is initialized by calling it with mode=-1.
For each grib record processed, the option-function is called with mode=verbosity index (verbosity ≥ 0).
After all grib records have been processed, the option-functions are told to clean up by calling
them with mode=-2.
Here is a sample function.
#include <stdio.h>
#include "grb2.h"
#include "wgrib2.h"
#include "fnlist.h"
extern int decode;
extern int need_output_file;
/*
* HEADER:100:min:inv:0:print minimum value
* the above line is needed by each command line option
* HEADER:sort-order:type-of-function:number-of-arguments:description
*/
int f_min(int mode, unsigned char **sec, float *data, int ndata, char *inv_out, void **local) {
double mn;
int ok, i;
if (mode == -1) decode = 1; // decode=1 so wgrib2 will unpack grib data
else {
mn = ok = 0;
for (i = 0; i < ndata; i++) {
if (!UNDEFINED_VAL(data[i])) {
if (ok) mn = mn < data[i] ? mn : data[i];
else { ok = 1; mn = data[i]; }
}
}
if (ok) sprintf(inv_out, "min=%lg",mn);
else sprintf(inv_out, "min=undefined");
}
return 0;
}
The arguments to f_min() are the standard for options that do not require an argument
mode = -1: initialization -2: cleanup O+: processing verbosity index
sec = sections of the grib (sub) message
*data = decoded grid point values
ndata = number of grid points
*inv_out = string that written to the inventory
**local = unique pointer, used for "static" variables.
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