Understanding some C++ coding practice [closed] - c++

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Closed 9 years ago.
I am currently trying to understand how the following code (http://pastebin.com/zTHUrmyx) works, my approach is currently compiling the software in debug and using gdb to step through the code.
However, I'm running into the problem that 'step' does not always tell me what is going on. Particularly unclear to me is the EXECUTE {...} which I cannot step into.
How do I go about learning what the code is doing?
1 /*
2 Copyright 2008 Brain Research Institute, Melbourne, Australia
3
4 Written by J-Donald Tournier, 27/06/08.
5
6 This file is part of MRtrix.
7
8 MRtrix is free software: you can redistribute it and/or modify
9 it under the terms of the GNU General Public License as published by
10 the Free Software Foundation, either version 3 of the License, or
11 (at your option) any later version.
12
13 MRtrix is distributed in the hope that it will be useful,
14 but WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 GNU General Public License for more details.
17
18 You should have received a copy of the GNU General Public License
19 along with 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 to manipulate data ordering within the image file
28
29 14-02-2010 J-Donald Tournier <d.tournier#brain.org.au>
30 * fix -coord option so that the "end" keyword can be 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 and optionally extract a subset of the input image.",
47 "If used correctly, this program can be a very useful workhorse. In addition to converting images between different formats, it can be used to extract specific studies from a data set, extract a specific region of interest, flip the images, or to scale the intensity of the 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 only at the 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 the voxel dimensions.")
71 .append (Argument ("sizes", "new dimensions", "A comma-separated list of values. Only those values specified will be changed. For example: 1,,3.5 will change the voxel size along the x & z axes, and leave the 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 to the intensity values.")
78 .append (Argument ("factor", "factor", "the factor by which to multiply the intensities.").type_float (NAN, NAN, 1.0)),
79
80 Option ("offset", "offset", "apply offset to the intensity values.")
81 .append (Argument ("bias", "bias", "the value of the offset.").type_float (NAN, NAN, 0.0)),
82
83 Option ("zero", "replace NaN by zero", "replace all NaN values with 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 the layout of the data in memory. The actual layout produced will depend on whether the output image format can support it.")
90 .append (Argument ("spec", "specifier", "the data layout specifier.").type_string ()),
91
92 Option ("prs", "DW gradient specified as PRS", "assume that the DW gradients are specified in the 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 do {
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); // zero
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 for (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() + "\" does not match image dimensions");
177
178 for (guint i = 0; i < 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 for (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 for (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 for 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 for (int n = 0; n < in_obj.ndim(); n++) {
206 if (pos[n].empty()) {
207 pos[n].resize (in_obj.dim(n));
208 for (guint i = 0; i < 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 for (int n = 0; n < in.ndim(); n++) in.set (n, pos[n][0]);
224
225 ProgressBar::init (out.voxel_count(), "copying data...");
226
227 do {
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 }

Answer 1

As was noted in the comments, EXECUTE seems to be a macro, apparent from the context a function header (and maybe a bit more, e.g. some global variables and functions), so the part in curly braces is the function body.
To get to the definition of EXECUTE, you will have to examine the headers.
However, if you can reach some part of the code during debugging, you could insert a string or char[] at that point, giving it the stringified version of EXECUTE, so you get whatever the preprocessor will emit for EXECUTE at that position in the code.
#define STR(x) #x
#define STRINGIFY(x) STR(x)
char c[] = STRINGIFY(EXECUTE);
the two macros are a known little macro trick to get the content of any macro as a string literal. Try it out and inspect the char array in your debugger to get the content of execute.
My wild guess here: EXECUTE is the main function or a replacement for it, the OPTIONS and ARGUMENTS describe what arguments the program expects and what command line options you can pass to it. Those macros and some of the used functions and variables (get_options, argument) are part of a little framework that should facilitate the usage, evaluation and user information about command line options.