Shapefile header analyser

analyser.c

#include <stdio.h>
#include <string.h>

int main(int argc, char *argv[])
{
    unsigned char headerBuffer[100];
    FILE *ptr;

    ptr = fopen(argv[1], "rb");

    fread(headerBuffer, sizeof(headerBuffer), 1, ptr);

    int fileCode = 
        (headerBuffer[0] << 24) +
        (headerBuffer[1] << 16) +
        (headerBuffer[2] << 8) +
        headerBuffer[3];

    int shpFileCode = 0x0000270a;

    if (fileCode == shpFileCode) {
        printf("Analysing shapefile\n");
    } else  {
        fprintf(stderr, "Error: file is not a shapefile. Exiting.");
        return 1;
    }

    int length =
        ((headerBuffer[24] << 24) +
        (headerBuffer[25] << 16) +
        (headerBuffer[26] << 8) +
        headerBuffer[27])
        << 1; // length is in 16 bit words; * 2 to get 8 bit bytes.

    printf("File length: %d bytes\n", length);

    int version =
        headerBuffer[28] +
        (headerBuffer[29] << 8) +
        (headerBuffer[30] << 16) +
        (headerBuffer[31] << 24);
    
    printf("Shapefile version: %d\n", version);

    int shapeType =
        headerBuffer[32] +       
        (headerBuffer[33] << 8) +
        (headerBuffer[34] << 16) +
        (headerBuffer[35] << 24);

    printf("Shape type: ");
    switch (shapeType) {
        case 0:  printf("Null shape");   break;
        case 1:  printf("Point");        break;
        case 3:  printf("Polyline");     break;
        case 5:  printf("Polygon");      break;
        case 8:  printf("MultiPoint");   break;
        case 11: printf("PointZ");       break;
        case 13: printf("PolylineZ");    break;
        case 15: printf("PolygonZ");     break;
        case 18: printf("MultiPointZ");  break;
        case 21: printf("PointM");       break;
        case 23: printf("PolylineM");    break;
        case 25: printf("PolygonM");     break;
        case 28: printf("MultiPointM");  break;
        case 31: printf("MultiPatch");   break;
    }
    printf("\n");

    return 0;
}