对于Unicode

Question

如何在C ++中获取字符串中的字符数？

Answer 1

如果您使用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，请拨打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"

Answer 2

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;
}

<强>输出：

Answer 3

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* - C风格的宽字符串
std::string - “标准”多字节字符串
std::wstring - “标准”宽字符串

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等等，其方法包括{{1} }，等等。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抽象了这一点，它可用于从任何类型获取字符串长度（和其他方面）。因此对于所有上述（包括非标准库）使用相同的函数.GetLength()。 This article描述了它是如何工作的，因为它并非完全明显或容易。

Answer 4

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运行时库中有strlen函数：

const char* p = "Hello";
size_t n = strlen(p);

Answer 5

如果您使用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);

Answer 6

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。

Answer 7

std::string str("a string");
std::cout << str.size() << std::endl;

Answer 8

表示实际的字符串对象：

yourstring.length();

或

yourstring.size();

Answer 9

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;
}

示例的输出是：

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

Answer 10

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;
}

不带空格的字符串

#include <iostream>
#include <string>
using namespace std;
int main(){
    string str;
    cin>>str;
    cout<<"Length of given string is"<<str.length();
    return 0;
}

Answer 11

对于Unicode

这里有几个答案可以解决，.length()对于多字节字符给出了错误的结果，但是有11个答案，但是没有一个提供解决方案。

Z͉̳̺ͥͬ̾a̴͕̲̒̒͌̋ͪl̨͎̰̘͉̟ͤ̀̈̚͜g͕͔̤͖̟̒͝ͅo̵̡̡̼͚̐ͯ̅ͪ̆ͣ̚案

首先，重要的是要了解“长度”的含义。例如，考虑字符串“ Z͉̳̺ͥͬ̾a̴͕̲̒̒͌̋ͪl̨͎̰̘͉̟ͤ̀̈̚͜g͕͔̤͖̟̒͝ͅo̵̡̡̼͚̐ͯ̅ͪ̆ͣ̚”（请注意，某些语言（尤其是泰语）实际上使用了结合的变音符号，因此这对于15岁的模因来说并不是唯一的用法，但显然那是最重要的用例）。假设它是用 UTF-8 编码的。我们可以通过3种方式讨论此字符串的长度：

95个字节

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    ...............

50个代码点

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

5个字素

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

使用ICU

查找长度

有一些用于ICU的C ++类，但是它们需要转换为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");
}

此打印：

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，并可能提供更好的接口。但是，它仍然需要与UTF-16进行相互转换。

Answer 12

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());

}

如何获取std :: string中的字符数？

12 个答案:

对于Unicode

Z͉̳̺ͥͬ̾a̴͕̲̒̒͌̋ͪl̨͎̰̘͉̟ͤ̀̈̚͜g͕͔̤͖̟̒͝ͅo̵̡̡̼͚̐ͯ̅ͪ̆ͣ̚案

95个字节

50个代码点

5个字素

使用ICU