#include <string>
#include <iostream>
int main()
{
std::string test("hello world ");
std::string label("label test");
test.append(&label[3]); //----- #1
std::cout << test << std::endl;
}
对于上面的代码,我期望的是“hello world e”,但实际上它的输出是“hello world el test”。它将位置3之后的所有字符附加到我的字符串test
。C++将一个字符从一个字符串追加到另一个字符串
在位置#1,如果我不把&迹象,会有编译错误:
str_append.cpp:10:10: error: no matching member function for call to 'append'
test.append(label[3]);
~~~~~^~~~~~
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:1516:19: note: candidate function not viable: no known conversion
from 'value_type' (aka 'char') to 'const value_type *' (aka 'const char *') for 1st argument; take the address of the argument with &
basic_string& append(const value_type* __s);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:1513:19: note: candidate function not viable: no known conversion
from 'value_type' (aka 'char') to 'const std::__1::basic_string<char>' for 1st argument
basic_string& append(const basic_string& __str);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:1525:9: note: candidate function template not viable: requires 2
arguments, but 1 was provided
append(_InputIterator __first, _InputIterator __last);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:1532:9: note: candidate function template not viable: requires 2
arguments, but 1 was provided
append(_ForwardIterator __first, _ForwardIterator __last);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:1515:19: note: candidate function not viable: requires 2
arguments, but 1 was provided
basic_string& append(const value_type* __s, size_type __n);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:1517:19: note: candidate function not viable: requires 2
arguments, but 1 was provided
basic_string& append(size_type __n, value_type __c);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:1514:19: note: candidate function not viable: requires at least 2
arguments, but 1 was provided
basic_string& append(const basic_string& __str, size_type __pos, size_type __n=npos);
^
1 error generated.
我能解决这个问题的唯一方法是将#1线更改为:
test += label[3];
所以,我想知道这背后的逻辑是什么? label[3]
不能返回单个字符吗?为什么它失败时,我只使用test.append(label[3]);
。为什么test += label[3];
成功?
在此先感谢。
又一个“我没看过文档”的问题。这个世界有什么问题? * downvotes和哭泣* –