argv []比较 [英] argv[] comparison
问题描述
进行argv []比较最安全的方法是什么？下面的代码
有效。
#include< iostream>
#include< string>
使用命名空间std;
int main（int argc，char * argv []）
{
字符串测试;
if（argc> 1）
test = argv [1];
if（test ==" NKDT"）
cout<< \ n比较是真的。让程序做点什么。\ n" ;;
else
cout<< \ n比较是错误的。让程序做别的事情。\ n" ;;
返回0;
}
* ka*****@hotmail.com ：
< blockquote class =post_quotes>
进行argv []比较最安全的方法是什么？下面的代码
有效。
#include< iostream>
#include< string>
使用命名空间std;
int main（int argc，char * argv []）
{
字符串测试;
if（argc> 1）
test = argv [1];
if（test ==" NKDT"）
cout<< \ n比较是真的。让程序做点什么。\ n" ;;
else
cout<< \ n比较是错误的。让程序做别的事情。\ n" ;;
返回0;
}
执行以下操作：
#include< iostream>
#include< cstddef>
＃ include< string>
#include< vector>
#include< stdexcept>
typedef std :: vector< ; std :: stringStringVector;
bool throwX（char const s []）{throw std :: runtime_error（s）; }
void cppMain（StringVector const& arguments）
{
arguments.size（）1
|| throwX（" usage：myprog ARG1"）;
if（arguments.at（1）==" NKDT"）
{
//做点什么。
}
其他
{
//做别的。
}
}
int main（int n，char * a []）
{
试试
{
cppMain（StringVector（a，a + n））;
返回EXIT_SUCCESS ;
}
catch（std :: exception const& x）
{
std :: cerr< ;< "！" << x.what（）<< std :: endl;
返回EXIT_FAILURE;
}
}
-
答：因为它弄乱了人们通常阅读文字的顺序。
问：为什么这么糟糕？
A：热门发布。
问：usenet和电子邮件中最烦人的事情是什么？
5月21日下午2:39，Alf P. Steinbach < a ... @ start.nowrote：
* kafe ... @ hotmail.com：
< blockquote class =post_quotes>
进行argv []比较最安全的方法是什么？下面的代码
有效。
#include< iostream>
#include< string>
using namespace std;
int main（int argc，char * argv []）
{
string测试;
if（argc> 1）
test = argv [1];
if（test ==" NKDT"）
cout<< \ n比较是真的。让程序做点什么。\ n" ;;
else
cout<< \ n比较是错误的。让程序做别的事情。\ n" ;;
返回0;
}
以下：
< snip>
OP的解决方案出了什么问题，看起来很多更多
简洁？
* da *********** @ fastmail.fm ：
5月21日下午2:39， Alf P. Steinbach < a ... @ start.nowrote：
> * kafe ... @ hotmail.com：
>>>
进行argv []比较最安全的方法是什么？下面的代码
有效。
#include< iostream>
#include< string>
使用命名空间std;
int main（int argc，char * argv []）
{
字符串测试;
if（argc> 1）
test = argv [1];
if（test ==" NKDT"）
cout<< \ n比较是真的。让程序做某事。\ n" ;;
其他
cout<< \ n比较是错误的。让程序执行其他操作。\ n" ;;
返回0;
}
执行以下操作：
< snip>
OP的解决方案出了什么问题，看起来更加简洁？b $ b简洁明了吗？
可能直接错误：始终表明程序成功
执行。也可能是直接错误：不处理异常。
但是，有人可能会设计一个程序，这样就不会有任何异常
传播到main并且如果它执行一个希望终止以便于调试，而不是报告和失败指示。所以它取决于设计
和方法和工具链以及某种程度上的个人偏好。
但我不认为这里缺乏异常处理是故意的。 />
Ungood：主要代码可以直接访问argc和argv，当目标
是以最安全的方式处理它们时（提供访问是不安全的）。另外
ungood一般：using namespace std：;。另外ungood：不使用
花括号用于嵌套语句（几乎任何样式指南都会
告诉你使用它们，总是，为了支持维护）。 />
简洁的外观：所有OP的代码都是程序特定的，
而我列出的代码主要是样板文件，一种
针对这种特殊小型学生计划的微框架或
专业人员的签出计划或一次性个人工具计划。
为了保持一致，可以写出例如（做/同/作为OP的代码）
#include< string>
#include< iostream>
int main（int n，char * a []）
{
using namespace std;
n 1&& std :: string（a [1]）==" NKDT"
？ cout<< \ n比较是真的。 Something.\\\
"
：cout<< \ n比较是错误的。其他东西。\ n" ;;
}
摆脱局部变量''test''以及''返回0''哪个
暗示（这是默认的）''main''，只是为了使它更加便宜
简洁我也删除了那个愚蠢的''其他''否则会耗尽
非常昂贵的行，而关键字''if''则需要阅读。我只是不明白为什么这么多程序员认为简洁是一个
的目标。他们最终没有理解他们自己的代码。
-
答：因为它弄乱了人们通常阅读文本的顺序。
问：为什么这么糟糕？
A：热门发布。
问：usenet和e中最烦人的事情是什么邮件？
What is the safest way to make an argv[] comparison? The code below
works.
#include <iostream>
#include <string>
using namespace std;
int main(int argc, char *argv[])
{
string test;
if(argc>1)
test = argv[1];
if(test=="NKDT")
cout << "\nComparison is true. Have program do something.\n";
else
cout << "\nComparison is false. Have program do something else.\n";
return 0;
}
* ka*****@hotmail.com:What is the safest way to make an argv[] comparison? The code below
works.
#include <iostream>
#include <string>
using namespace std;
int main(int argc, char *argv[])
{
string test;
if(argc>1)
test = argv[1];
if(test=="NKDT")
cout << "\nComparison is true. Have program do something.\n";
else
cout << "\nComparison is false. Have program do something else.\n";
return 0;
}Do the following:
#include <iostream>
#include <cstddef>
#include <string>
#include <vector>
#include <stdexcept>
typedef std::vector<std::stringStringVector;
bool throwX( char const s[] ) { throw std::runtime_error( s ); }
void cppMain( StringVector const& arguments )
{
arguments.size() 1
|| throwX( "usage: myprog ARG1" );
if( arguments.at(1) == "NKDT" )
{
// Do something.
}
else
{
// Do something else.
}
}
int main( int n, char* a[] )
{
try
{
cppMain( StringVector( a, a+n ) );
return EXIT_SUCCESS;
}
catch( std::exception const& x )
{
std::cerr << "!" << x.what() << std::endl;
return EXIT_FAILURE;
}
}
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
On May 21, 2:39 pm, "Alf P. Steinbach" <a...@start.nowrote:* kafe...@hotmail.com:
What is the safest way to make an argv[] comparison? The code below
works.
#include <iostream>
#include <string>
using namespace std;
int main(int argc, char *argv[])
{
string test;
if(argc>1)
test = argv[1];
if(test=="NKDT")
cout << "\nComparison is true. Have program do something.\n";
else
cout << "\nComparison is false. Have program do something else.\n";
return 0;
}
Do the following:<snip>
What was wrong with the OP''s solution, which appeared to be much more
concise?
* da***********@fastmail.fm:On May 21, 2:39 pm, "Alf P. Steinbach" <a...@start.nowrote:>* kafe...@hotmail.com:>>>
What is the safest way to make an argv[] comparison? The code below
works.
#include <iostream>
#include <string>
using namespace std;
int main(int argc, char *argv[])
{
string test;
if(argc>1)
test = argv[1];
if(test=="NKDT")
cout << "\nComparison is true. Have program do something.\n";
else
cout << "\nComparison is false. Have program do something else.\n";
return 0;
}Do the following:
<snip>
What was wrong with the OP''s solution, which appeared to be much more
concise?Probably directly wrong: always indicating success for the program
execution. Also probably directly wrong: doesn''t handle exceptions.
However, one might design a program so that no exception should ever
propagate up to main and if it does one wants termination for ease of
debugging, not a report and failure indication. So it depends on design
and methodology and toolchain and to some extent personal preference.
But I don''t think the lack of exception handling here was intentional.
Ungood: the main code has direct access to argc and argv, when the aim
is to handle them in "the safest way" (giving access is unsafe). Also
ungood in general: "using namespace std:;". Also ungood: not using
curly braces for nested statements (just about any style guideline will
tell you to use them, always, in order to support maintenance).
Appearance of conciseness: all of the OP''s code is program-specific,
whereas the code I listed is mostly boilerplate, a kind of
micro-framework for this particular kind of small student program or
professional''s check-it-out program or single-use personal tool program.
For consisness one could write e.g. (doing the /same/ as the OP''s code)
#include <string>
#include <iostream>
int main( int n, char* a[] )
{
using namespace std;
n 1 && std::string( a[1] ) == "NKDT"
? cout << "\nComparison is true. Something.\n"
: cout << "\nComparison is false. Something else.\n";
}
getting rid of the local variable ''test'' and also the ''return 0'' which
is implied (it''s the default) in ''main'', and just to make it extra
concise I also removed that darned ''else'' which otherwise would use up a
very expensive line, and the keyword ''if'' which is so much to read. I
simply don''t understand why so many programmers think conciseness is a
goal. They just end up not understanding their own code.
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
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