C++ 将 int 附加到 std::string
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Append an int to a std::string
提问by Hakon89
Why is this code gives an Debug Assertion Fail?
为什么此代码给出调试断言失败？
std::string query;
int ClientID = 666;
query = "select logged from login where id = ";
query.append((char *)ClientID);
回答by hmjd
The std::string::append()method expects its argument to be a NULL terminated string (char*).
该std::string::append()方法期望它的参数是一个 NULL 终止的字符串 ( char*)。
There are several approaches for producing a stringcontaing an int:
有几种方法可以生成string包含 an int：
#include <sstream> std::ostringstream s; s << "select logged from login where id = " << ClientID; std::string query(s.str());std::to_string(C++11)std::string query("select logged from login where id = " + std::to_string(ClientID));#include <boost/lexical_cast.hpp> std::string query("select logged from login where id = " + boost::lexical_cast<std::string>(ClientID));
#include <sstream> std::ostringstream s; s << "select logged from login where id = " << ClientID; std::string query(s.str());std::to_string(C++11)std::string query("select logged from login where id = " + std::to_string(ClientID));#include <boost/lexical_cast.hpp> std::string query("select logged from login where id = " + boost::lexical_cast<std::string>(ClientID));
回答by luke
You cannot cast an int to a char* to get a string. Try this:
您不能将 int 转换为 char* 来获取字符串。尝试这个：
std::ostringstream sstream;
sstream << "select logged from login where id = " << ClientID;
std::string query = sstream.str();
回答by Bojan Komazec
I have a feeling that your ClientIDis not of a string type (zero-terminated char*or std::string) but some integral type (e.g. int) so you need to convert number to the string first:
我有一种感觉，您ClientID的不是字符串类型（以零结尾char*或std::string），而是某种整数类型（例如int），因此您需要先将数字转换为字符串：
std::stringstream ss;
ss << ClientID;
query.append(ss.str());
But you can use operator+as well (instead of append):
但是你也可以使用operator+（而不是append）：
query += ss.str();
回答by WeaselFox
You are casting ClientIDto char* causing the function to assume its a null terinated char array, which it is not.
您正在转换ClientID为 char* 导致该函数假定其为空终止字符数组，而事实并非如此。
from cplusplus.com :
来自 cplusplus.com ：
string& append ( const char * s ); Appends a copy of the string formed by the null-terminated character sequence (C string) pointed by s. The length of this character sequence is determined by the first ocurrence of a null character (as determined by traits.length(s)).
string& append ( const char * s ); 附加由 s 指向的空终止字符序列（C 字符串）形成的字符串的副本。此字符序列的长度由空字符的第一次出现确定（由 traits.length(s) 确定）。
