debugging - Understanding some C++ coding practice -

i trying understand how following code (http://pastebin.com/zthurmyx) works, approach compiling software in debug , using gdb step through code.

however, i'm running problem 'step' not tell me going on. particularly unclear me execute {...} cannot step into.

how go learning code doing?

   1     /*    2     copyright 2008 brain research institute, melbourne, australia    3    4     written j-donald tournier, 27/06/08.    5    6     file part of mrtrix.    7    8     mrtrix free software: can redistribute and/or modify    9     under terms of gnu general public license published   10     free software foundation, either version 3 of license, or   11     (at option) later version.   12   13     mrtrix distributed in hope useful,   14     without warranty; without implied warranty of   15     merchantability or fitness particular purpose.  see   16     gnu general public license more details.   17   18     should have received copy of gnu general public license   19     along mrtrix.  if not, see <http://www.gnu.org/licenses/>.   20   21   22     15-10-2008 j-donald tournier <d.tournier@brain.org.au>   23     * fix -prs option handling   24     * remove mr::dicom_dw_gradients_prs flag   25   26     15-10-2008 j-donald tournier <d.tournier@brain.org.au>   27     * add -layout option manipulate data ordering within image file   28   29     14-02-2010 j-donald tournier <d.tournier@brain.org.au>   30     * fix -coord option "end" keyword can used   31   32   33 */   34   35 #include "app.h"   36 #include "image/position.h"   37 #include "image/axis.h"   38 #include "math/linalg.h"   39   40 using namespace std;   41 using namespace mr;   42   43 set_version_default;   44   45 description = {   46   "perform conversion between different file types , optionally extract subset of input image.",   47   "if used correctly, program can useful workhorse. in addition converting images between different formats, can used extract specific studies data set, extract specific region of interest, flip images, or scale intensity of images.",   48   null   49 };   50   51 arguments = {   52   argument ("input", "input image", "the input image.").type_image_in (),   53   argument ("ouput", "output image", "the output image.").type_image_out (),   54   argument::end   55 };   56   57   58 const gchar* type_choices[] = { "real", "imag", "mag", "phase", "complex", null };   59 const gchar* data_type_choices[] = { "float32", "float32le", "float32be", "float64", "float64le", "float64be",   60     "int32", "uint32", "int32le", "uint32le", "int32be", "uint32be",   61     "int16", "uint16", "int16le", "uint16le", "int16be", "uint16be",   62     "cfloat32", "cfloat32le", "cfloat32be", "cfloat64", "cfloat64le", "cfloat64be",   63     "int8", "uint8", "bit", null };   64   65 options = {   66   option ("coord", "select coordinates", "extract data @ coordinates specified.", false, true)   67     .append (argument ("axis", "axis", "the axis of interest").type_integer (0, int_max, 0))   68     .append (argument ("coord", "coordinates", "the coordinates of interest").type_sequence_int()),   69   70   option ("vox", "voxel size", "change voxel dimensions.")   71     .append (argument ("sizes", "new dimensions", "a comma-separated list of values. values specified changed. example: 1,,3.5 change voxel size along x & z axes, , leave y-axis voxel size unchanged.")   72         .type_sequence_float ()),   73   74   option ("datatype", "data type", "specify output image data type.")   75     .append (argument ("spec", "specifier", "the data type specifier.").type_choice (data_type_choices)),   76   77   option ("scale", "scaling factor", "apply scaling intensity values.")   78     .append (argument ("factor", "factor", "the factor multiply intensities.").type_float (nan, nan, 1.0)),   79   80   option ("offset", "offset", "apply offset intensity values.")   81     .append (argument ("bias", "bias", "the value of offset.").type_float (nan, nan, 0.0)),   82   83   option ("zero", "replace nan zero", "replace nan values zero."),   84   85   option ("output", "output type", "specify type of output")   86     .append (argument ("type", "type", "type of output.")   87         .type_choice (type_choices)),   88   89   option ("layout", "data layout", "specify layout of data in memory. actual layout produced depend on whether output image format can support it.")   90     .append (argument ("spec", "specifier", "the data layout specifier.").type_string ()),   91   92   option ("prs", "dw gradient specified prs", "assume dw gradients specified in prs frame (siemens dicom only)."),   93   94   option::end   95 };   96   97   98   99 inline bool next (image::position& ref, image::position& other, const std::vector<int>* pos)  100 {  101   int axis = 0;  102   {  103     ref.inc (axis);  104     if (ref[axis] < ref.dim(axis)) {  105       other.set (axis, pos[axis][ref[axis]]);  106       return (true);  107     }  108     ref.set (axis, 0);  109     other.set (axis, pos[axis][0]);  110     axis++;  111   } while (axis < ref.ndim());  112   return (false);  113 }  114  115  116  117  118  119 execute {  120   std::vector<optbase> opt = get_options (1); // vox  121   std::vector<float> vox;  122   if (opt.size())  123     vox = parse_floats (opt[0][0].get_string());  124  125  126   opt = get_options (3); // scale  127   float scale = 1.0;  128   if (opt.size()) scale = opt[0][0].get_float();  129  130   opt = get_options (4); // offset  131   float offset = 0.0;  132   if (opt.size()) offset = opt[0][0].get_float();  133  134   opt = get_options (5); // 0  135   bool replace_nan = opt.size();  136  137   opt = get_options (6); // output  138   image::outputtype output_type = image::default;  139   if (opt.size()) {  140     switch (opt[0][0].get_int()) {  141       case 0: output_type = image::real; break;  142       case 1: output_type = image::imaginary; break;  143       case 2: output_type = image::magnitude; break;  144       case 3: output_type = image::phase; break;  145       case 4: output_type = image::realimag; break;  146     }  147   }  148  149  150  151  152   image::object &in_obj (*argument[0].get_image());  153  154   image::header header (in_obj);  155  156   if (output_type == 0) {  157     if (in_obj.is_complex()) output_type = image::realimag;  158     else output_type = image::default;  159   }  160  161   if (output_type == image::realimag) header.data_type = datatype::cfloat32;  162   else if (output_type == image::phase) header.data_type = datatype::float32;  163   else header.data_type.unset_flag (datatype::complexnumber);  164  165    166   opt = get_options (2); // datatype  167   if (opt.size()) header.data_type.parse (data_type_choices[opt[0][0].get_int()]);  168  169   (guint n = 0; n < vox.size(); n++)  170     if (isfinite (vox[n])) header.axes.vox[n] = vox[n];  171  172   opt = get_options (7); // layout  173   if (opt.size()) {  174     std::vector<image::axis> ax = parse_axes_specifier (header.axes, opt[0][0].get_string());  175     if (ax.size() != (guint) header.axes.ndim())  176       throw exception (string("specified layout \"") + opt[0][0].get_string() + "\" not match image dimensions");  177  178     (guint = 0; < ax.size(); i++) {  179       header.axes.axis[i] = ax[i].axis;  180       header.axes.forward[i] = ax[i].forward;  181     }  182   }  183  184  185   opt = get_options (8); // prs  186   if (opt.size() && header.dw_scheme.rows() && header.dw_scheme.columns()) {  187     (guint row = 0; row < header.dw_scheme.rows(); row++) {  188       double tmp = header.dw_scheme(row, 0);  189       header.dw_scheme(row, 0) = header.dw_scheme(row, 1);  190       header.dw_scheme(row, 1) = tmp;  191       header.dw_scheme(row, 2) = -header.dw_scheme(row, 2);  192     }  193   }  194  195   std::vector<int> pos[in_obj.ndim()];  196  197   opt = get_options (0); // coord  198   (guint n = 0; n < opt.size(); n++) {  199     int axis = opt[n][0].get_int();  200     if (pos[axis].size()) throw exception ("\"coord\" option specified twice axis " + str (axis));  201     pos[axis] = parse_ints (opt[n][1].get_string(), header.dim(axis)-1);  202     header.axes.dim[axis] = pos[axis].size();  203   }  204  205   (int n = 0; n < in_obj.ndim(); n++) {  206     if (pos[n].empty()) {  207       pos[n].resize (in_obj.dim(n));  208       (guint = 0; < pos[n].size(); i++) pos[n][i] = i;  209     }  210   }  211  212  213   in_obj.apply_scaling (scale, offset);  214  215  216  217  218  219  220   image::position in (in_obj);  221   image::position out (*argument[1].get_image (header));  222  223   (int n = 0; n < in.ndim(); n++) in.set (n, pos[n][0]);  224  225   progressbar::init (out.voxel_count(), "copying data...");  226  227   {  228  229     float re, im = 0.0;  230     in.get (output_type, re, im);  231     if (replace_nan) if (gsl_isnan (re)) re = 0.0;  232     out.re (re);  233  234     if (output_type == image::realimag) {  235       if (replace_nan) if (gsl_isnan (im)) im = 0.0;  236       out.im (im);  237     }  238  239     progressbar::inc();  240   } while (next (out, in, pos));  241  242   progressbar::done();  243 } 

as noted in comments, execute seems macro, apparent context function header (and maybe bit more, e.g. global variables , functions), part in curly braces function body.

to definition of execute, have examine headers.

however, if can reach part of code during debugging, insert string or char[] @ point, giving stringified version of execute, whatever preprocessor emit execute at position in code.

#define str(x) #x #define stringify(x) str(x) char c[] = stringify(execute); 

the 2 macros known little macro trick content of macro string literal. try out , inspect char array in debugger content of execute.

my wild guess here: execute main function or replacement it, options , arguments describe arguments program expects , command line options can pass it. macros , of used functions , variables (get_options, argument) part of little framework should facilitate usage, evaluation , user information command line options.