C++ 习惯性地拆分字符串\u视图
我读了这本书,很喜欢它简洁的回答。现在我想对string_视图执行同样的操作。问题是,C++ 习惯性地拆分字符串\u视图,c++,c++17,string-view,C++,C++17,String View,我读了这本书,很喜欢它简洁的回答。现在我想对string_视图执行同样的操作。问题是,stringstream无法获取string\u视图: #include <iostream> #include <string> #include <sstream> #include <algorithm> #include <iterator> int main() { using namespace std; string_v
stringstream
无法获取string\u视图
:
#include <iostream>
#include <string>
#include <sstream>
#include <algorithm>
#include <iterator>
int main() {
using namespace std;
string_view sentence = "And I feel fine...";
istringstream iss(sentence); // <== error
copy(istream_iterator<string_view>(iss),
istream_iterator<string_view>(),
ostream_iterator<string_view>(cout, "\n"));
}
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int main(){
使用名称空间std;
string_view句子=“我感觉很好…”;
istringstream iss(句子);//如果要使用该特定方法,只需将字符串视图
转换为字符串
,明确地:
istringstream iss{string(sentence)}; // N.B. braces to avoid most vexing parse
copy(istream_iterator<string>(iss),
istream_iterator<string>(),
ostream_iterator<string_view>(cout, "\n"));
istringstream iss{string(句子)};//N.B.大括号以避免最麻烦的解析
复制(istream_迭代器(iss),
istream_迭代器(),
ostream_迭代器(cout,“\n”);
C++标准库没有良好的字符串操作功能。您可能想查看哪些是可用的,等等。其中任何一个都比这个好。<> >代码> String Strue/COD>拥有它所运行的字符串。这意味着它创建给定字符串的副本。它不能仅引用字符串。
即使建议使用基于string\u视图
的流
类型,流仍然不是随机访问范围。它们无法处理字符串的子范围。这就是为什么它们通过复制而不是通过迭代器或其他方式从流中提取数据
您需要的最好是通过基于regex
的机制来完成,因为这样做不需要复制任何内容。它们与string\u视图
s配合使用(尽管您必须手动构建string\u视图
s)。用分隔符分割,然后返回一个向量
设计用于快速拆分.csv
文件中的行
在MSVC 2017 v15.9.6
和英特尔编译器v19.0
下测试,使用C++17
编译(这是string\u视图
所必需的)
#include <string_view>
std::vector<std::string_view> Split(const std::string_view str, const char delim = ',')
{
std::vector<std::string_view> result;
int indexCommaToLeftOfColumn = 0;
int indexCommaToRightOfColumn = -1;
for (int i=0;i<static_cast<int>(str.size());i++)
{
if (str[i] == delim)
{
indexCommaToLeftOfColumn = indexCommaToRightOfColumn;
indexCommaToRightOfColumn = i;
int index = indexCommaToLeftOfColumn + 1;
int length = indexCommaToRightOfColumn - index;
// Bounds checking can be omitted as logically, this code can never be invoked
// Try it: put a breakpoint here and run the unit tests.
/*if (index + length >= static_cast<int>(str.size()))
{
length--;
}
if (length < 0)
{
length = 0;
}*/
std::string_view column(str.data() + index, length);
result.push_back(column);
}
}
const std::string_view finalColumn(str.data() + indexCommaToRightOfColumn + 1, str.size() - indexCommaToRightOfColumn - 1);
result.push_back(finalColumn);
return result;
}
// Google Test integrates into VS2017 if ReSharper is installed.
#include "gtest/gtest.h" // Can install using vcpkg
// In main(), call:
// ::testing::InitGoogleTest(&argc, argv);return RUN_ALL_TESTS();
TEST(Strings, Split)
{
{
const std::string str = "A,B,C";
auto tokens = Split(str, ',');
EXPECT_TRUE(tokens.size() == 3);
EXPECT_TRUE(tokens[0] == "A");
EXPECT_TRUE(tokens[1] == "B");
EXPECT_TRUE(tokens[2] == "C");
}
{
const std::string str = ",B,C";
auto tokens = Split(str, ',');
EXPECT_TRUE(tokens.size() == 3);
EXPECT_TRUE(tokens[0] == "");
EXPECT_TRUE(tokens[1] == "B");
EXPECT_TRUE(tokens[2] == "C");
}
{
const std::string str = "A,B,";
auto tokens = Split(str, ',');
EXPECT_TRUE(tokens.size() == 3);
EXPECT_TRUE(tokens[0] == "A");
EXPECT_TRUE(tokens[1] == "B");
EXPECT_TRUE(tokens[2] == "");
}
{
const std::string str = "";
auto tokens = Split(str, ',');
EXPECT_TRUE(tokens.size() == 1);
EXPECT_TRUE(tokens[0] == "");
}
{
const std::string str = "A";
auto tokens = Split(str, ',');
EXPECT_TRUE(tokens.size() == 1);
EXPECT_TRUE(tokens[0] == "A");
}
{
const std::string str = ",";
auto tokens = Split(str, ',');
EXPECT_TRUE(tokens.size() == 2);
EXPECT_TRUE(tokens[0] == "");
EXPECT_TRUE(tokens[1] == "");
}
{
const std::string str = ",,";
auto tokens = Split(str, ',');
EXPECT_TRUE(tokens.size() == 3);
EXPECT_TRUE(tokens[0] == "");
EXPECT_TRUE(tokens[1] == "");
EXPECT_TRUE(tokens[2] == "");
}
{
const std::string str = "A,";
auto tokens = Split(str, ',');
EXPECT_TRUE(tokens.size() == 2);
EXPECT_TRUE(tokens[0] == "A");
EXPECT_TRUE(tokens[1] == "");
}
{
const std::string str = ",B";
auto tokens = Split(str, ',');
EXPECT_TRUE(tokens.size() == 2);
EXPECT_TRUE(tokens[0] == "");
EXPECT_TRUE(tokens[1] == "B");
}
}