how to convert from int to char*?

问题

The only way I know is:

#include <sstream>
#include <string.h>
using namespace std;

int main() {
  int number=33;
  stringstream strs;
  strs << number;
  string temp_str = strs.str();
  char* char_type = (char*) temp_str.c_str();
}

But is there any method with less typing ?

回答1:

In C++17, use std::to_chars as:

std::array<char, 10> str;
std::to_chars(str.data(), str.data() + str.size(), 42);

In C++11, use std::to_string as:

std::string s = std::to_string(number);
char const *pchar = s.c_str();  //use char const* as target type

And in C++03, what you're doing is just fine, except use const as:
```
char const* pchar = temp_str.c_str(); //dont use cast
```

回答2:

I think you can use a sprintf :

int number = 33;
char* numberstring[(((sizeof number) * CHAR_BIT) + 2)/3 + 2];
sprintf(numberstring, "%d", number);

回答3:

You can use boost

#include <boost/lexical_cast.hpp>
string s = boost::lexical_cast<string>( number );

回答4:

C-style solution could be to use itoa, but better way is to print this number into string by using sprintf / snprintf. Check this question: How to convert an integer to a string portably?

Note that itoa function is not defined in ANSI-C and is not part of C++, but is supported by some compilers. It's a non-standard function, thus you should avoid using it. Check this question too: Alternative to itoa() for converting integer to string C++?

Also note that writing C-style code while programming in C++ is considered bad practice and sometimes referred as "ghastly style". Do you really want to convert it into C-style char* string? :)

回答5:

I would not typecast away the const in the last line since it is there for a reason. If you can't live with a const char* then you better copy the char array like:

char* char_type = new char[temp_str.length()];
strcpy(char_type, temp_str.c_str());

回答6:

See this answer https://stackoverflow.com/a/23010605/2760919

For your case, just change the type in snprintf from long ("%ld") to int ("%n").

回答7:

You also can use casting.

example:

string s;
int value = 3;
s.push_back((char)('0' + value));

回答8:

This might be a bit late, but i also had the same issue. Converting to char was addressed in C++17 with the "charconv" library.

https://en.cppreference.com/w/cpp/utility/to_chars

回答9:

Alright.. firstly I needed something that did what this question is asking, but I needed it FAST! Unfortunately the "better" way is nearly 600 lines of code!!! Pardon the name of it that doesn't have anything to do with what it's doing. Proper name was Integer64ToCharArray(int64_t value);

https://github.com/JeremyDX/All-Language-Testing-Code/blob/master/C%2B%2B%20Examples/IntegerToCharArrayTesting.cpp

Feel free to try cleaning that code up without hindering performance.

Input: Any signed 64 bit value from min to max range.

Example:

std::cout << "Test: " << AddDynamicallyToBuffer(LLONG_MAX) << '\n';
std::cout << "Test: " << AddDynamicallyToBuffer(LLONG_MIN) << '\n';

Output:

Test: 9223372036854775807
Test: -9223372036854775808

Original Speed Tests: (Integer64ToCharArray();)

Best case 1 digit value.

Loops: 100,000,000, Time Spent: 1,381(Milli), Time Per Loop 13(Nano)

Worse Case 20 Digit Value.

Loops: 100,000,000, Time Spent: 22,656(Milli), Time Per Loop 226(Nano

New Design Speed Tests: (AddDynamicallyToBuffer();)

Best case 1 digit value.

Loops: 100,000,000, Time Spent: 427(Milli), Time Per Loop 4(Nano)

32 Bit Worst Case - 11 digit Value.

Loops: 100,000,000, Time Spent: 1,991(Milli), Time Per Loop 19(Nano)

Negative 1 Trillion Worst Case - 14 digit Value.

Loops: 100,000,000, Time Spent: 5,681(Milli), Time Per Loop 56(Nano)

64 Bit Worse Case - 20 Digit Value.

Loops: 100,000,000, Time Spent: 13,148(Milli), Time Per Loop 131(Nano)

How It Works!

We Perform a Divide and Conquer technique and once we now the maximum length of the string we simply set each character value individually. As shown in above speed tests the larger lengths get big performance penalties, but it's still far faster then the original loop method and no code has actually changed between the two methods other then looping is no longer in use.

In my usage hence the name I return the offset instead and I don't edit a buffer of char arrays rather I begin updating vertex data and the function has an additional parameter for offset so it's not initialized to -1.

来源：https://stackoverflow.com/questions/10847237/how-to-convert-from-int-to-char

标签

c++

integer

const-char