我在尝试检查if语句中的多种可能性时遇到了问题。
用户输入一个字符串，然后我针对多种可能性检查该字符串。
if (theString == "Seven" || "seven" || "7")
{
theInt = 7;
cout << "You chose: " << theInt << endl;
}
else if (theString == "Six" || "six" || "6")
{
theInt = 6;
cout << "You chose: " << theInt << endl;
}
所以我只想简单地说明我要完成的任务。在我的程序中，这些if语句在函数中，我正在使用#include [string]。 （我甚至不确定“6”或“7”是否可行，但我现在甚至无法测试我的代码:( 所以现在在我的代码中，如果用户输入6，我的程序将运行并为theInt分配值7。有什么想法吗？
感谢。
答案 0 :(得分：6)
我认为变量theString的类型是std::string。否则至少这个比较
theString == "Seven"
没有意义，
if语句中的条件
if (theString == "Seven" || "seven" || "7")
相当于
if ( ( theString == "Seven" ) || ( "seven" ) || ( "7" ) )
并始终产生true，因为至少字符串文字"seven"的地址不等于零。因此，此子表达式( "seven" )提供整个表达式将等于true。
你应该写
if (theString == "Seven" || theString == "seven" || theString == "7")
但最初将字符串转换为大写或小写更好。
例如
#include <algorithm>
#include <string>
#include <cstring>
//...
std::transform(theString.begin(), theString.end(), theString.begin(),
[](char c) { return std::toupper((unsigned char)c); });
if (theString == "SEVEN" || theString == "7")
{
theInt = 7;
cout << "You chose: " << theInt << endl;
}
else if ( theString == "SIX" || theString == "6" )
{
theInt = 6;
cout << "You chose: " << theInt << endl;
}
答案 1 :(得分：3)
您无法将变量与多个值进行比较，就像您应该在C ++中那样：
if (theString == "Seven" || theString == "seven" || theString == "7")
{
theInt = 7;
cout << "You chose: " << theInt << endl;
}
else if (theString == "Six" || theString == "six" || theString == "6")
{
theInt = 6;
cout << "You chose: " << theInt << endl;
}
答案 2 :(得分：2)
更新2017-04-22 - 在下面添加了代码示例
这是识别在实施过程中找到的派生需求的典型示例。我建议你考虑编写一个函数来支持它。
从
改变if (theString == "Seven" || "seven" || "7")
{
//....
（这是无效的c ++，因为if条件总是为真）
更改为
if (0 == compare(theString, "Seven", "seven", "7")
{
//....
并声明并实现类似
的内容// return 0 when theString matches at least one patX
// else return -1
int compare(const std::string& theString,
const char* pat0, // no default, must provide
const char* pat1 = nullptr,
const char* pat2 = nullptr,
const char* pat3 = nullptr,
const char* pat4 = nullptr
/* add as many patX as you desire */)
{
if (0 == theString.compare(pat0)) return 0; // found a match
//
// ignore nullptr patterns
if (nullptr != pat1) && (0 == theString.compare(pat1)) {
return(0);
}
if(nullptr != pat2) && (0 == theString.compare(pat2)) {
return(0);
}
// ...
// when get to end with no match
return (-1); // indicate no match to any of patterns
}
我其实更喜欢以下内容。上面有点像strstr（），其中使用了std :: string
的更多功能int compare(const std::string& theString, // what you are given
const std::string& patterns) // concatenated list of search patterns
{
//..
}
您可以调用
if (0 == compare(theString, "Seven seven SEVEN 7")
{
//
实现必须梳理空格分隔的模式..但这并不困难，并且可以很容易地在循环中实现，因此不需要对要测试的比较进行限制。
您应该何时考虑创建一个新功能以支持新的衍生重新获取？
我可以在识别3个或更多用途时创建新功能。 祝你好运。
更新2017-04-22
找到我几年前写的一些代码，修复了它，添加了演示......
代码编译并且似乎运行，但很少测试。
dtb :: T471_t提供私人方法供您查看。
size_t compare（const std :: string s，std :: string patterns）
size_t grep（const std :: string pfn，const std :: string patterns， 的std :: ostream的和放; an_ostream = std :: cout）
- 使用compare（）
size_t cpuinfoGet（）
- 使用grep
- “wc＆lt; / proc / cpuinfo”（ubuntu上的“众所周知的文件”）在我的2台核心机器上报告54行，更多内核，更多行
size_t coreCountGet（）
- 使用grep（）
- 创建nullDev以抑制grep正常输出
#include <chrono>
#include <fstream>
#include <iostream>
#include <sstream>
#include <string>
#include <cassert>
// 'compressed' chrono access --------------vvvvvvv
typedef std::chrono::high_resolution_clock HRClk_t; // std-chrono-hi-res-clk
typedef HRClk_t::time_point Time_t; // std-chrono-hi-res-clk-time-point
typedef std::chrono::microseconds US_t; // std-chrono-microseconds
using namespace std::chrono_literals; // support suffixes like 100ms
// examples:
//
// Time_t start_us = HRClk_t::now();
//
// auto duration_us = std::chrono::duration_cast<US_t>(HRClk_t::now() - start_us);
// auto count_us = duration_us.count();
// or
// std::cout << " complete " << duration_us.count() << " us" << std::endl;
namespace dtb
{
class T471_t
{
const std::string dashLine = (" --------------------------------------------------------------");
public:
T471_t() = default;
~T471_t() = default;
int exec()
{
std::cout << "\n cpuinfoGet()\n" << dashLine << std::endl;
(void)cpuinfoGet(); // uses grep which uses compare
std::cout << dashLine << std::endl;
// count of lines which contain "processor" in linux file "/proc/cpuinfo"
std::cout << "\n\n " << coreCountGet()
<< " cores on this system. (coreCountGet())\n\n" << std::endl;
return(0);
}
private: // methods
// returns std::string::npos when none of the patterns found,
// else returns index of earliest found patterns of space delimited substr in
size_t compare (const std::string& s,
std::string patterns) // pass by value
{
size_t found = std::string::npos;
size_t patCount = 0;
std::stringstream ssPat(patterns + ' '); // load patterns into ram based stringstream
// ^^^^^ -- getline() can cause eof() in this
const char delim = ' '; // see getline()
do
{
if(0 == patterns.size()) break; // no patterns to search for, kick out
if(0 == s.size()) break; // no string in which to search, kick out
do {
std::string pat;
(void)std::getline(ssPat, pat, delim); // extract 1 space delimited pattern
if(false == ssPat.good())
{
if(ssPat.eof()) break; // quitely exit, a normal op
// let user know of patten problem
std::cerr << "\n err pattern extract: " << patterns
<< " (" << patCount << ')' << std::endl;
break;
}
patCount += 1;
//trimLeadingWhiteSpace(patterns); // tbr
//trimTrailingWhiteSpace(patterns); // tbr
if(0 == patterns.size()) break; // no more patterns
// search s for pat
found = s.find(pat);
if(found != std::string::npos) break; // one of the patterns found in s
} while(1); // repeat until 1 found or all patterns tried
}while(0);
return(found);
} // size_t compare (const std::string& s, std::string patterns)
size_t grep(const std::string pfn,
const std::string patterns, // concatenated list of search patterns
std::ostream& an_ostream = std::cout) // redirectable
{
size_t foundCount = 0;
an_ostream << " grep (" << pfn << ", [" << patterns
<< "] )" << std::endl;
do
{
std::ifstream infile(pfn);
if(!infile.is_open())
{
an_ostream << pfn << " not found.\n" << std::endl; // tbr - std::cerr?
break; // skip over file op's (no close needed)
}
do
{
if(infile.eof()) break; // file empty?
std::string lineIn;
(void)getline(infile, lineIn); // default delimiter is \n
if (0 == lineIn.size()) continue; // empty line?
size_t found = compare(lineIn, patterns); // any of patterns in lineIn?
if(std::string::npos != found) // found at least one pattern
{
an_ostream << " " << lineIn << std::endl; // found it, print it
foundCount += 1;
}
// else no pattern found - continue until eof of inFil
} while(1);
infile.close();
}while(0);
return(foundCount);
} // size_t grep(const std::string pfn, const std::string patterns, std::ostream& an_ostream = std::cout)
// space delimited list of ---^^^^^^^^
size_t cpuinfoGet()
{
size_t count = grep("/proc/cpuinfo", // pfn
"bogomips model name processor"); // patterns to search for
std::cout << "\n info lines: " << count << std::endl;
return(count);
} // size_t cpuinfoGet(void)
size_t coreCountGet()
{
// create a no-ouptput output
std::ofstream nullDev; // and do not open
nullDev.setstate(std::ios_base::badbit); // set error, ignore errors, do not close
size_t retVal = grep(std::string("/proc/cpuinfo"),
std::string("processor"), // line count of "processor" is core count
nullDev); // nullDev -- no output
return(retVal);
} // size_t coreCountGet()(void)
}; // class T471_t
} // namespace dtb
int main(int /*argc*/, char** /*argv[]*/)
{
Time_t start_us = HRClk_t::now();
int retVal = -1;
{
dtb::T471_t t471;
retVal = t471.exec();
}
auto duration_us = std::chrono::duration_cast<US_t>(HRClk_t::now() - start_us);
std::cout << " FINI " << duration_us.count() << " us" << std::endl;
return(retVal);
}
输出：
cpuinfoGet()
--------------------------------------------------------------
grep (/proc/cpuinfo, [bogomips model name processor] )
processor : 0
model : 75
model name : AMD Athlon(tm) 64 X2 Dual Core Processor 5000+
bogomips : 4809.67
processor : 1
model : 75
model name : AMD Athlon(tm) 64 X2 Dual Core Processor 5000+
bogomips : 4809.67
info lines: 8
--------------------------------------------------------------
2 cores on this system. (coreCountGet())
FINI 829 us
答案 3 :(得分：1)
有时，数据可能是比代码更好的解决方案。
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
static final String DB_URL = "jdbc:mysql://localhost:3306/medicinedb";
static final String USER = "root";
static final String PASS = "";
static final String DRIVER = "com.mysql.jdbc.Driver";
public boolean saveMedicine(List<MedicineName> medicineName) throws ClassNotFoundException {
Connection conn = null;
Statement stmt = null;
try {
Class.forName(DRIVER);
//STEP 3: Open a connection
System.out.println("Connecting to database...");
conn = DriverManager.getConnection(DB_URL, USER, PASS);
//STEP 4: Execute a query
System.out.println("Creating statement...");
stmt = conn.createStatement();
for (MedicineName element : medicineName) {
String sql;
sql = " insert into medicinename (name, pgurl)" + " values
( ?, ?)";
System.out.println(conn);
PreparedStatement preparedStmt = conn.prepareStatement(sql);
preparedStmt.setString(1, element.getName());
preparedStmt.setString(2, element.getPgurl());
stmt.executeUpdate(sql);
}
stmt.close();
conn.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return true;
}
正如弗拉德所说，你可能最好先转换为小写。这个答案就是将代码直接转换为数据。请注意，对于缺少的字符串，此答案将使用默认值0;你的代码遗漏了这样的默认值。
答案 4 :(得分：1)
使用std::set和c ++ 11，您可以使用与。
检查一下：
#include <iostream>
#include <string>
#include <set>
int main()
{
if( (std::set<std::string>{"Seven", "seven", "7"}).count("seven") )
{
std::cout << "foo\n";
}
std::string theString("6");
if( (std::set<std::string>{"Six", "six", "6"}).count(theString) )
{
std::cout << "bar\n";
}
}