Add command-line utilities "offsets.c" and "extract.c" for use in

low-level analyzsis of database files.

FossilOrigin-Name: dfa22ed4387f9526b74d5265503c7c8e9d559903

tool/extract.c

@@ -0,0 +1,46 @@
+/*
+** Extract a range of bytes from a file.
+**
+** Usage:
+**
+**    extract FILENAME OFFSET AMOUNT
+**
+** The bytes are written to standard output.
+*/
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(int argc, char **argv){
+  FILE *f;
+  char *zBuf;
+  int ofst;
+  int n;
+  size_t got;
+
+  if( argc!=4 ){
+    fprintf(stderr, "Usage: %s FILENAME OFFSET AMOUNT\n", *argv);
+    return 1;
+  }
+  f = fopen(argv[1], "rb");
+  if( f==0 ){
+    fprintf(stderr, "cannot open \"%s\"\n", argv[1]);
+    return 1;
+  }
+  ofst = atoi(argv[2]);
+  n = atoi(argv[3]);
+  zBuf = malloc( n );
+  if( zBuf==0 ){
+    fprintf(stderr, "out of memory\n");
+    return 1;
+  }
+  fseek(f, ofst, SEEK_SET);
+  got = fread(zBuf, 1, n, f);
+  fclose(f);
+  if( got<n ){
+    fprintf(stderr, "got only %d of %d bytes\n", got, n);
+    return 1;
+  }else{
+    fwrite(zBuf, 1, n, stdout);
+  }
+  return 0;
+}