[英]c-style string sorting with sort and qsort
I'm trying to use both sort and qsort to sort a c-style string and them see which of them is better, so I've written this code, but it is not working , so can you please tell me what is wrong with it. 我正在尝试使用sort和qsort来排序一个c风格的字符串,他们看到哪个更好,所以我写了这个代码,但它没有用,所以你能告诉我有什么问题吗?它。 thanks in advance.
提前致谢。
#include <iostream>
#include<vector>
#include<cstdlib>
#include<algorithm>
#include<cstring>
#include<chrono>
#include<string>
#include<sstream>
using namespace std;
using namespace std::chrono;
void bvect(vector<double> &vec, int num)
{
auto gen = bind(normal_distribution<double>(15,4.0),default_random_engine());
for(int i=0; i<num; ++i)
vec.push_back(gen());
}
char* converttostring(int number)
{
stringstream ss;
ss << number;
return (ss.c_str());
}
int cst_cmp(const void *one, const void *two)
{
char a = *((char*)one);
char b = *((char*)two);
return strcmp(a, b);
}
//Generated random strings
void textvect(vector<string> &vec, int num)
{
srand(time(NULL));
for(int i=0; i<num; ++i)
vec.push_back(converttostring(rand()%num +1));
}
void displayvector(vector<char*>vect)
{
for (int i=0; i<vect.size(); ++i){
for (int j=0; j<strlen(vect[i]); ++j)
cout<<vect[i][j];
cout<<endl;
}
}
int main(){
int sz=100000;
vector<char*>text1, text2;
textvect(text1, sz);
text2.resize(text1.size());
copy(text1.begin(),text1.end(),text2.begin());
// qsort() string
auto t1 = system_clock::now();
qsort(&text1[0], text1.size(), sizeof(char*), cst_cmp);
auto t2 = system_clock::now();
auto dms = duration_cast<milliseconds>(t2-t1);
cout << "string qsort() took " << dms.count() << " milliseconds\n";
// sort() string
auto t3 = system_clock::now();
std::sort(text2.begin(), text2.end());
auto t4 = system_clock::now();
auto dms1 = duration_cast<milliseconds>(t4-t3);
cout << "string sort() took " << dms1.count() << " milliseconds\n";
return 0;
}
For std::sort
, you are just using the default comparator, which will just compare pointer values. 对于
std::sort
,您只使用默认比较器,它只比较指针值。 You need to pass a comparator that does a proper comparison (using strcmp, for example): 您需要传递一个比较器,进行适当的比较(例如,使用strcmp):
std::sort(text2.begin(), text2.end(),
[](const char* lhs, const char* rhs) { return strcmp(lhs,rhs) < 0; });
That's one problem, there may be others. 这是一个问题,可能还有其他问题。
One problem is in your compare function for qsort
: 一个问题是
qsort
的比较函数:
int cst_cmp(const void *one, const void *two)
{
char a = *((char*)one);
char b = *((char*)two);
return strcmp(a, b);
}
You are not comparing strings here, because a
and b
are just chars. 你不是在这里比较字符串,因为
a
和b
只是字符。 You might as well avoid them: 你也可以避免它们:
int cst_cmp(const void *one, const void *two)
{
return (strcmp(*(char **)one, *(char **)two));
}
These are the errors I obtain trying to compile your code: 这些是我尝试编译代码时遇到的错误:
> g++ main.cc -std=c++0x
main.cc: In function ‘char* converttostring(int)’:
main.cc:24:15: error: ‘std::stringstream’ has no member named ‘c_str’
main.cc: In function ‘int cst_cmp(const void*, const void*)’:
main.cc:31:23: error: invalid conversion from ‘char’ to ‘const char*’ [-fpermissive]
/usr/include/string.h:143:12: error: initializing argument 1 of ‘int strcmp(const char*, const char*)’ [-fpermissive]
main.cc:31:23: error: invalid conversion from ‘char’ to ‘const char*’ [-fpermissive]
/usr/include/string.h:143:12: error: initializing argument 2 of ‘int strcmp(const char*, const char*)’ [-fpermissive]
main.cc: In function ‘int main()’:
main.cc:55:23: error: invalid initialization of reference of type ‘std::vector<std::basic_string<char> >&’ from expression of type ‘std::vector<char*>’
main.cc:35:6: error: in passing argument 1 of ‘void textvect(std::vector<std::basic_string<char> >&, int)’
24:15 c_str()
is a member function of string
not of stringstream
. 24:15
c_str()
是string
不是stringstream
的成员函数。 See here . 看到这里 。
31:23 strcmp()
wants two const char *
not two char
. 31:23
strcmp()
想要两个const char *
而不是两个char
。 See here . 看到这里 。
55:23 and 35:6 char*
is not the same type as string
. 55:23和35:6
char*
与string
类型不同。
This function isn't working 此功能无效
char* converttostring(int number)
{
stringstream ss;
ss << number;
return (ss.c_str());
}
and if it was sort of fixed ( ss.str().c_str()
), it would return a pointer to a temporary. 如果它是一种固定的(
ss.str().c_str()
),它将返回一个指向临时的指针。
If you have a compiler with some C++11 support, you can use std::to_string
from the standard library. 如果您的编译器支持某些C ++ 11,则可以使用标准库中的
std::to_string
。 Otherwise, change the return type to std::string
(no pointer!). 否则,将返回类型更改为
std::string
(无指针!)。
问Stroustrup;)只是为C字符串数组分配空间并输入字符ino it ..记得解除分配它..
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