如何在C ++中获取字符串中的字符数？
如果您使用的是std::string，请致电length()：
std::string str = "hello";
std::cout << str << ":" << str.length();
// Outputs "hello:5"
如果您使用的是c字符串，请调用strlen()。
const char *str = "hello";
std::cout << str << ":" << strlen(str);
// Outputs "hello:5"
或者，如果你碰巧喜欢使用Pascal风格的字符串（或f *****字符串作为Joel Spolsky likes to call them，当它们有一个尾随的NULL）时，只需取消引用第一个字符。
const char *str = "\005hello";
std::cout << str + 1 << ":" << *str;
// Outputs "hello:5"
获取字符串长度而不打扰std命名空间的最简单方法如下
带/不带空格的字符串
#include <iostream>
#include <string>
using namespace std;
int main(){
string str;
getline(cin,str);
cout<<"Length of given string is"<<str.length();
return 0;
}
字符串没有空格
#include <iostream>
#include <string>
using namespace std;
int main(){
string str;
cin>>str;
cout<<"Length of given string is"<<str.length();
return 0;
}
这里有几个答案已经解决了.length()用多字节字符给出了错误的结果，但有11个答案，但没有一个提供解决方案。
首先，通过“长度”知道你的意思很重要。对于一个激励性的例子，考虑字符串“Z͉̳̺ͥͬ̾a̴͕̒̒͌̋ͪl̨͎̰̘͉̟ͤ̈̚͜g͕͔̤͖̟̒͝o̵̡̡̼͚̐ͯ̅ͪ̆ͣ̚”（注意一些语言，特别是泰语，实际上使用组合变音符号，所以这不仅对15岁的模因有用，但显然这是最重要的用例） 。假设它以UTF-8编码。我们可以通过3种方式讨论这个字符串的长度：
00000000: 5acd a5cd accc becd 89cc b3cc ba61 cc92 Z............a..
00000010: cc92 cd8c cc8b cdaa ccb4 cd95 ccb2 6ccd ..............l.
00000020: a4cc 80cc 9acc 88cd 9ccc a8cd 8ecc b0cc ................
00000030: 98cd 89cc 9f67 cc92 cd9d cd85 cd95 cd94 .....g..........
00000040: cca4 cd96 cc9f 6fcc 90cd afcc 9acc 85cd ......o.........
00000050: aacc 86cd a3cc a1cc b5cc a1cc bccd 9a ...............
LATIN CAPITAL LETTER Z
COMBINING LEFT ANGLE BELOW
COMBINING DOUBLE LOW LINE
COMBINING INVERTED BRIDGE BELOW
COMBINING LATIN SMALL LETTER I
COMBINING LATIN SMALL LETTER R
COMBINING VERTICAL TILDE
LATIN SMALL LETTER A
COMBINING TILDE OVERLAY
COMBINING RIGHT ARROWHEAD BELOW
COMBINING LOW LINE
COMBINING TURNED COMMA ABOVE
COMBINING TURNED COMMA ABOVE
COMBINING ALMOST EQUAL TO ABOVE
COMBINING DOUBLE ACUTE ACCENT
COMBINING LATIN SMALL LETTER H
LATIN SMALL LETTER L
COMBINING OGONEK
COMBINING UPWARDS ARROW BELOW
COMBINING TILDE BELOW
COMBINING LEFT TACK BELOW
COMBINING LEFT ANGLE BELOW
COMBINING PLUS SIGN BELOW
COMBINING LATIN SMALL LETTER E
COMBINING GRAVE ACCENT
COMBINING DIAERESIS
COMBINING LEFT ANGLE ABOVE
COMBINING DOUBLE BREVE BELOW
LATIN SMALL LETTER G
COMBINING RIGHT ARROWHEAD BELOW
COMBINING LEFT ARROWHEAD BELOW
COMBINING DIAERESIS BELOW
COMBINING RIGHT ARROWHEAD AND UP ARROWHEAD BELOW
COMBINING PLUS SIGN BELOW
COMBINING TURNED COMMA ABOVE
COMBINING DOUBLE BREVE
COMBINING GREEK YPOGEGRAMMENI
LATIN SMALL LETTER O
COMBINING SHORT STROKE OVERLAY
COMBINING PALATALIZED HOOK BELOW
COMBINING PALATALIZED HOOK BELOW
COMBINING SEAGULL BELOW
COMBINING DOUBLE RING BELOW
COMBINING CANDRABINDU
COMBINING LATIN SMALL LETTER X
COMBINING OVERLINE
COMBINING LATIN SMALL LETTER H
COMBINING BREVE
COMBINING LATIN SMALL LETTER A
COMBINING LEFT ANGLE ABOVE
Z with some s**t
a with some s**t
l with some s**t
g with some s**t
o with some s**t
ICU有C ++类，但它们需要转换为UTF-16。您可以直接使用C类型和宏来获得一些UTF-8支持：
#include <memory>
#include <iostream>
#include <unicode/utypes.h>
#include <unicode/ubrk.h>
#include <unicode/utext.h>
//
// C++ helpers so we can use RAII
//
// Note that ICU internally provides some C++ wrappers (such as BreakIterator), however these only seem to work
// for UTF-16 strings, and require transforming UTF-8 to UTF-16 before use.
// If you already have UTF-16 strings or can take the performance hit, you should probably use those instead of
// the C functions. See: http://icu-project.org/apiref/icu4c/
//
struct UTextDeleter { void operator()(UText* ptr) { utext_close(ptr); } };
struct UBreakIteratorDeleter { void operator()(UBreakIterator* ptr) { ubrk_close(ptr); } };
using PUText = std::unique_ptr<UText, UTextDeleter>;
using PUBreakIterator = std::unique_ptr<UBreakIterator, UBreakIteratorDeleter>;
void checkStatus(const UErrorCode status)
{
if(U_FAILURE(status))
{
throw std::runtime_error(u_errorName(status));
}
}
size_t countGraphemes(UText* text)
{
// source for most of this: http://userguide.icu-project.org/strings/utext
UErrorCode status = U_ZERO_ERROR;
PUBreakIterator it(ubrk_open(UBRK_CHARACTER, "en_us", nullptr, 0, &status));
checkStatus(status);
ubrk_setUText(it.get(), text, &status);
checkStatus(status);
size_t charCount = 0;
while(ubrk_next(it.get()) != UBRK_DONE)
{
++charCount;
}
return charCount;
}
size_t countCodepoints(UText* text)
{
size_t codepointCount = 0;
while(UTEXT_NEXT32(text) != U_SENTINEL)
{
++codepointCount;
}
// reset the index so we can use the structure again
UTEXT_SETNATIVEINDEX(text, 0);
return codepointCount;
}
void printStringInfo(const std::string& utf8)
{
UErrorCode status = U_ZERO_ERROR;
PUText text(utext_openUTF8(nullptr, utf8.data(), utf8.length(), &status));
checkStatus(status);
std::cout << "UTF-8 string (might look wrong if your console locale is different): " << utf8 << std::endl;
std::cout << "Length (UTF-8 bytes): " << utf8.length() << std::endl;
std::cout << "Length (UTF-8 codepoints): " << countCodepoints(text.get()) << std::endl;
std::cout << "Length (graphemes): " << countGraphemes(text.get()) << std::endl;
std::cout << std::endl;
}
void main(int argc, char** argv)
{
printStringInfo(u8"Hello, world!");
printStringInfo(u8"หวัดดีชาวโลก");
printStringInfo(u8"\xF0\x9F\x90\xBF");
printStringInfo(u8"Z͉̳̺ͥͬ̾a̴͕̲̒̒͌̋ͪl̨͎̰̘͉̟ͤ̀̈̚͜g͕͔̤͖̟̒͝ͅo̵̡̡̼͚̐ͯ̅ͪ̆ͣ̚");
}
这打印：
UTF-8 string (might look wrong if your console locale is different): Hello, world!
Length (UTF-8 bytes): 13
Length (UTF-8 codepoints): 13
Length (graphemes): 13
UTF-8 string (might look wrong if your console locale is different): หวัดดีชาวโลก
Length (UTF-8 bytes): 36
Length (UTF-8 codepoints): 12
Length (graphemes): 10
UTF-8 string (might look wrong if your console locale is different): 🐿
Length (UTF-8 bytes): 4
Length (UTF-8 codepoints): 1
Length (graphemes): 1
UTF-8 string (might look wrong if your console locale is different): Z͉̳̺ͥͬ̾a̴͕̲̒̒͌̋ͪl̨͎̰̘͉̟ͤ̀̈̚͜g͕͔̤͖̟̒͝ͅo̵̡̡̼͚̐ͯ̅ͪ̆ͣ̚
Length (UTF-8 bytes): 95
Length (UTF-8 codepoints): 50
Length (graphemes): 5
Boost.Locale包装ICU，并可能提供更好的界面。但是，它仍然需要转换为UTF-16 /从UTF-16转换。
这可能是输入字符串并查找其长度的最简单方法。
// Finding length of a string in C++
#include<iostream>
#include<string>
using namespace std;
int count(string);
int main()
{
string str;
cout << "Enter a string: ";
getline(cin,str);
cout << "\nString: " << str << endl;
cout << count(str) << endl;
return 0;
}
int count(string s){
if(s == "")
return 0;
if(s.length() == 1)
return 1;
else
return (s.length());
}
在处理C ++字符串（std :: string）时，您正在寻找length()或size()。两者都应该为您提供相同的价值。但是在处理C-Style字符串时，您将使用strlen()。
#include <iostream>
#include <string.h>
int main(int argc, char **argv)
{
std::string str = "Hello!";
const char *otherstr = "Hello!"; // C-Style string
std::cout << str.size() << std::endl;
std::cout << str.length() << std::endl;
std::cout << strlen(otherstr) << std::endl; // C way for string length
std::cout << strlen(str.c_str()) << std::endl; // convert C++ string to C-string then call strlen
return 0;
}
输出：
6
6
6
6
这取决于你所谈论的字符串类型。有许多类型的字符串：
const char* - C风格的多字节字符串const wchar_t* - 一种C风格的宽弦std::string - 一个“标准”多字节字符串std::wstring - “标准”宽弦对于3和4，您可以使用.size()或.length()方法。
对于1，您可以使用strlen()，但必须确保字符串变量不是NULL（=== 0）
对于2，您可以使用wcslen()，但必须确保字符串变量不是NULL（=== 0）
非标准C ++库中还有其他字符串类型，例如MFC的CString，ATL的CComBSTR，ACE的ACE_CString等，以及.GetLength()等方法。我无法记住它们的具体细节。
STLSoft库已经用他们所谓的string access shims抽象出来了，它可以用来获取任何类型的字符串长度（以及其他方面）。所以对于以上所有（包括非标准库）使用相同的函数stlsoft::c_str_len()。 This article描述了它是如何工作的，因为它并非完全明显或容易。
如果您使用旧的C风格字符串而不是较新的STL样式字符串，那么C运行时库中就有strlen函数：
const char* p = "Hello";
size_t n = strlen(p);
如果您使用的是std :: string，则有两种常用方法：
std::string Str("Some String");
size_t Size = 0;
Size = Str.size();
Size = Str.length();
如果您使用的是C样式字符串（使用char *或const char *），那么您可以使用：
const char *pStr = "Some String";
size_t Size = strlen(pStr);
string foo;
... foo.length() ...
.length和.size是同义词，我只是认为“长度”是一个稍微清晰的词。
std::string str("a string");
std::cout << str.size() << std::endl;
对于实际的字符串对象：
yourstring.length();
要么
yourstring.size();
在C ++ std :: string中，length（）和size（）方法为您提供了字节数，而不一定是字符数！与c-Style sizeof（）函数相同！
对于大多数可打印的7bit-ASCII字符，这是相同的值，但对于不是7bit-ASCII的字符，它绝对不是。请参阅以下示例以获得实际结果（64位Linux）。
没有简单的c / c ++函数可以真正计算字符数。顺便说一句，所有这些东西都是依赖于实现的，在其他环境中可能会有所不同（编译器，win 16/32，linux，embedded，...）
请参阅以下示例：
#include <string>
#include <iostream>
#include <stdio.h>
#include <string.h>
using namespace std;
int main()
{
/* c-Style char Array */
const char * Test1 = "1234";
const char * Test2 = "ÄÖÜ€";
const char * Test3 = "αβγ𝄞";
/* c++ string object */
string sTest1 = "1234";
string sTest2 = "ÄÖÜ€";
string sTest3 = "αβγ𝄞";
printf("\r\nC Style Resluts:\r\n");
printf("Test1: %s, strlen(): %d\r\n",Test1, (int) strlen(Test1));
printf("Test2: %s, strlen(): %d\r\n",Test2, (int) strlen(Test2));
printf("Test3: %s, strlen(): %d\r\n",Test3, (int) strlen(Test3));
printf("\r\nC++ Style Resluts:\r\n");
cout << "Test1: " << sTest1 << ", Test1.size(): " <<sTest1.size() <<" sTest1.length(): " << sTest1.length() << endl;
cout << "Test1: " << sTest2 << ", Test2.size(): " <<sTest2.size() <<" sTest1.length(): " << sTest2.length() << endl;
cout << "Test1: " << sTest3 << ", Test3.size(): " <<sTest3.size() << " sTest1.length(): " << sTest3.length() << endl;
return 0;
}
该示例的输出是这样的：
C Style Results:
Test1: ABCD, strlen(): 4
Test2: ÄÖÜ€, strlen(): 9
Test3: αβγ𝄞, strlen(): 10
C++ Style Results:
Test1: ABCD, sTest1.size(): 4 sTest1.length(): 4
Test2: ÄÖÜ€, sTest2.size(): 9 sTest2.length(): 9
Test3: αβγ𝄞, sTest3.size(): 10 sTest3.length(): 10