(原創) 如何為程式碼加上行號? (C/C++) (STL)
Abstract
若需要將程式碼放進word交報告或做文件時，或許我們會想將程式碼加上行號方便講解，如同博客園顯示程式碼那樣，我們該如何做呢?
Introduction
使用環境：Visual C++ 9.0 / Visual Studio 2008
一段C++的小程式，可以幫程式碼加上行號後輸出。
map_code_line.cpp / C++
1 /*
2 (C) OOMusou 2008 http://oomusou.cnblogs.com
3
4 Filename : map_code_line.cpp
5 Compiler : Visual C++ 9.0 / Visual Studio 2008
6 Description : Demo how to add line number for code
7 Release : 07/18/2008 1.0
8 */
9 #include <iostream>
10 #include <fstream>
11 #include <string>
12 #include <map>
13 #include <algorithm>
14
15 using namespace std;
16
17 ifstream infile("map_code_line.cpp");
18 ofstream outfile("map_code_line_r.cpp");
19
20 struct print_map {
21 void operator() (pair<int, string> p) {
22 cout << p.first << " " << p.second << endl;
23 outfile << p.first << " " << p.second << endl;
24 }
25 };
26
27 int main() {
28 map<int, string> lines;
29
30 string line;
31 int line_num = 1;
32 while(getline(infile, line))
33 lines[line_num++] = line;
34
35 infile.close();
36
37 for_each(lines.begin(), lines.end(), print_map());
38 outfile.close();
39 }
2 (C) OOMusou 2008 http://oomusou.cnblogs.com
3
4 Filename : map_code_line.cpp
5 Compiler : Visual C++ 9.0 / Visual Studio 2008
6 Description : Demo how to add line number for code
7 Release : 07/18/2008 1.0
8 */
9 #include <iostream>
10 #include <fstream>
11 #include <string>
12 #include <map>
13 #include <algorithm>
14
15 using namespace std;
16
17 ifstream infile("map_code_line.cpp");
18 ofstream outfile("map_code_line_r.cpp");
19
20 struct print_map {
21 void operator() (pair<int, string> p) {
22 cout << p.first << " " << p.second << endl;
23 outfile << p.first << " " << p.second << endl;
24 }
25 };
26
27 int main() {
28 map<int, string> lines;
29
30 string line;
31 int line_num = 1;
32 while(getline(infile, line))
33 lines[line_num++] = line;
34
35 infile.close();
36
37 for_each(lines.begin(), lines.end(), print_map());
38 outfile.close();
39 }
執行結果
1 /*
2 (C) OOMusou 2008 http://oomusou.cnblogs.com
3
4 Filename : map_code_line.cpp
5 Compiler : Visual C++ 9.0 / Visual Studio 2008
6 Description : Demo how to add line number for code
7 Release : 07/18/2008 1.0
8 */
9 #include <iostream>
10 #include <fstream>
11 #include <string>
12 #include <map>
13 #include <algorithm>
14
15 using namespace std;
16
17 ifstream infile("map_code_line.cpp");
18 ofstream outfile("map_code_line_r.cpp");
19
20 struct print_map {
21 void operator() (pair<int, string> p) {
22 cout << p.first << " " << p.second << endl;
23 outfile << p.first << " " << p.second << endl;
24 }
25 };
26
27 int main() {
28 map<int, string> lines;
29
30 string line;
31 int line_num = 1;
32 while(getline(infile, line))
33 lines[line_num++] = line;
34
35 infile.close();
36
37 for_each(lines.begin(), lines.end(), print_map());
38 outfile.close();
39 }
2 (C) OOMusou 2008 http://oomusou.cnblogs.com
3
4 Filename : map_code_line.cpp
5 Compiler : Visual C++ 9.0 / Visual Studio 2008
6 Description : Demo how to add line number for code
7 Release : 07/18/2008 1.0
8 */
9 #include <iostream>
10 #include <fstream>
11 #include <string>
12 #include <map>
13 #include <algorithm>
14
15 using namespace std;
16
17 ifstream infile("map_code_line.cpp");
18 ofstream outfile("map_code_line_r.cpp");
19
20 struct print_map {
21 void operator() (pair<int, string> p) {
22 cout << p.first << " " << p.second << endl;
23 outfile << p.first << " " << p.second << endl;
24 }
25 };
26
27 int main() {
28 map<int, string> lines;
29
30 string line;
31 int line_num = 1;
32 while(getline(infile, line))
33 lines[line_num++] = line;
34
35 infile.close();
36
37 for_each(lines.begin(), lines.end(), print_map());
38 outfile.close();
39 }
32行
while(getline(infile, line))
lines[line_num++] = line;
lines[line_num++] = line;
是整個程式的關鍵：使用map，key存放行號，value存放每一行的程式碼。而且隨著每一行程式碼的讀入，自動增加行號。
37行
for_each(lines.begin(), lines.end(), print_map());
將map內容印出，因為map無法配合copy()，只好退而求其次使用for_each()與functor。
20行
struct print_map {
void operator() (pair<int, string> p) {
cout << p.first << " " << p.second << endl;
outfile << p.first << " " << p.second << endl;
}
};
void operator() (pair<int, string> p) {
cout << p.first << " " << p.second << endl;
outfile << p.first << " " << p.second << endl;
}
};
配合for_each()的functor，22行的cout可以拿掉，只是方面在螢幕顯示而已。
Conclusion
STL的map是很好用的容器，尤其substring寫法，若index下沒有元素，會自動新增，所以才會有lines[line_number++] = line;這麼漂亮的寫法。
See Also
(原創) 將map輸出到cout，是否有更方便的方法? (C/C++) (STL)
(原創) 如何使用Function Object? (C/C++) (STL)
(原創) Function Pointer、Delegate和Function Object (C/C++) (template) (.NET) (C#)
(原創) 如何正確的使用迴圈(使用for_each)? (C/C++) (STL) (template)
