Sorry, but I know how to do it in other languages, but C is rather new to me. I need to import an ascii grid file in a C code. The structure of the file is as follows:

ncols 12
nrows 101
xllcorner 2.0830078125
yllcorner 39.35908297583665
cellsize 0.00439453125
nodata_value -2147483648
401.99 407.38 394.17 362.35 342.36 335.13 319.91 284.99 262.88 259.58 245.62 233.58
397.63 396.36 380.70 358.96 339.35 327.96 314.06 296.73 279.11 264.80 257.20 249.97
389.71 381.29 356.41 338.75 326.04 323.36 317.67 301.30 281.79 269.46 261.94 250.72
.....

I can read the bulk of values but I am struggling to properly import the first 6 lines in two arrays, a character one (namevar) and a double one (valvar). My only partially working code is:

#define ny      101
#define nx      12
#define dime    nx *ny
int main(void)
{
    FILE   *dem;
    double Z[dime], varval[6];

    char namevar[12];
    int  l = 1;

    dem = fopen("buttami.txt", "r");
    int i;
    int j;

    while (l < 7)
    {
        //
        fscanf(dem, "%s %f\n", &namevar, &varval[l]);
        printf("%s %.8f\n", namevar, varval[l]);

        l  ;
    }
    for (i = 1; i < dime; i  )
    {
        fscanf(dem, "%lf", &Z[i]);
        printf("%.5f ", Z[i]);

        printf("\n");
    }

    fclose(dem);
}

CodePudding user response：

Comments address many issue, this focuses on your specific mention...

"I am struggling to properly import the first 6 lines in two arrays, a character one (namevar) and a double one (valvar)"

First, the variable char namevar[12]; is too small to contain the longest name string it will need to contain: "nodata_value" as stored in the file contains 12 characters requiring the variable namevar to be created with size of at least 13 to provide room for the null terminator. ( see definition of C string )

The top part of the input file could be thought of as a header section, and its content as tag/values. An array of struct is useful to store content of varying types into a single array, each containing a set of members to accommodate the various types, in this case one C string, and one double. For example:

typedef struct {
   char namevar[20];
   double varval;
} header_s;

header_s header[6] = {0};//array of 6, each element contains two members,
                         //1 a char array with room for null terminator for field name
                         //1 a double to contain value

Then your fscanf() loop will look like this:

     //note changes to format specifier and the 
     //string member needs no &  
     int l=0;//C uses zero base indexing
     dem=fopen("buttami.txt", "r");
     if(dem)//test for success before using
     {
         while(l<6){//zero base indexing again (0-5)
             if(fscanf(dem,"%s %lf", header[l].namevar,&header[l].varval) == 2)
             {
                 printf("%s %.8f\n",header[l].namevar,header[l].varval);
             } //else handle error
             l  ;
         }
         fclose(dem);
     }

CodePudding user response：

By your example data description, I guess it is Arc/Info Ascii Grid foramt by wikipedia https://en.wikipedia.org/wiki/Esri_grid.

For raster data files I/O, please try library Gdal. Gdal doc about this format https://gdal.org/drivers/raster/aaigrid.html

Here is code samples for open and read a raster file https://gdal.org/tutorials/raster_api_tut.html