我应该如何在C++中获取字符串的字符数量?
我应该如何在C++中获取字符串的字符数量?
std::string
,调用 length()
函数。std::string str = "hello";
std::cout << str << ":" << str.length();
// Outputs "hello:5"
如果您正在使用C字符串,请调用strlen()
函数。
const char *str = "hello";
std::cout << str << ":" << strlen(str);
// Outputs "hello:5"
或者,如果你偏爱使用帕斯卡风格的字符串(或者像Joel Spolsky在这篇文章中所说的,“f ***** strings”是指它们具有尾随的NULL),只需引用第一个字符。
const char *str = "\005hello";
std::cout << str + 1 << ":" << *str;
// Outputs "hello:5"
std::size_t
会增加价值。 - chux - Reinstate Monica处理C++字符串(std::string)时,您需要使用length()或size()。两者都应该提供相同的值。然而,在处理C风格的字符串时,您需要使用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;
}
输出结果:
6
6
6
6
这里有几个回答提到.length()
在多字节字符时会给出错误的结果,但是有11个答案没有给出解决方案。
首先,重要的是要知道你所说的“长度”是什么意思。举个例子,考虑字符串“Z͉̳̺ͥͬ̾a̴͕̲̒̒͌̋ͪl̨͎̰̘͉̟ͤ̀̈̚͜g͕͔̤͖̟̒͝ͅo̵̡̡̼͚̐ͯ̅ͪ̆ͣ̚”(请注意,一些语言,尤其是泰语,实际上使用组合变音符号,因此这不仅仅适用于15岁的模因,但显然这是最重要的用例)。假设它是以UTF-8编码的。我们可以用3种方式来谈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
虽然ICU有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");
}
这将打印:
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包装了ICU,可能提供更好的接口。但是,它仍需要进行UTF-16的转换。
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.size()
或.length()
方法。strlen()
,但必须确保字符串变量不为NULL(=== 0)。wcslen()
,但必须确保字符串变量不为NULL(=== 0)。CString
,ATL的CComBSTR
,ACE的ACE_CString
等,具有诸如.GetLength()
等方法。我不能立即记住它们所有的细节。
STLSoft库使用所谓的字符串访问shim将所有这些抽象出来,可以用于从任何类型获取字符串长度(和其他方面)。因此,对于上述所有内容(包括非标准库),都可以使用相同的函数stlsoft::c_str_len()
。本文描述了它是如何工作的,因为它并不完全明显或容易。
#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;
}
下面是示例的输出结果:
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
std::string Str("Some String");
size_t Size = 0;
Size = Str.size();
Size = Str.length();
如果您正在使用C风格的字符串(使用char *或const char *),那么您可以使用以下代码:
const char *pStr = "Some String";
size_t Size = strlen(pStr);
如果你正在使用旧的C风格字符串而不是较新的STL风格字符串,那么C运行时库中有一个strlen
函数:
const char* p = "Hello";
size_t n = strlen(p);
string foo;
... foo.length() ...
.length和.size是同义词,我只是认为"length"这个词更清晰明了。
std::string str("a string");
std::cout << str.size() << std::endl;
对于一个实际的字符串对象:
yourstring.length();
或者
yourstring.size();