C语言字符串转int、long、long long:
int atoi( const char *str );
long atol( const char *str );
long long atoll( const char *str );
#include <iostream>
#include <cstdlib>
int main(){
const char *str1 = "42";
const char *str2 = "3.14159";
const char *str3 = "31337 with words";
const char *str4 = "words and 2";
int num1 = std::atoi(str1);
int num2 = std::atoi(str2);
int num3 = std::atoi(str3);
int num4 = std::atoi(str4);
std::cout << "std::atoi(\"" << str1 << "\") is " << num1 << '\n';
std::cout << "std::atoi(\"" << str2 << "\") is " << num2 << '\n';
std::cout << "std::atoi(\"" << str3 << "\") is " << num3 << '\n';
std::cout << "std::atoi(\"" << str4 << "\") is " << num4 << '\n';
}
C++ string转int、long、long long:
int stoi( const std::string& str, std::size_t* pos = 0, int base = 10 );
int stoi( const std::wstring& str, std::size_t* pos = 0, int base = 10 );
long stol( const std::string& str, std::size_t* pos = 0, int base = 10 );
long stol( const std::wstring& str, std::size_t* pos = 0, int base = 10 );
long long stoll( const std::string& str, std::size_t* pos = 0, int base = 10 );
long long stoll( const std::wstring& str, std::size_t* pos = 0, int base = 10 );
str |
- |
the string to convert |
pos |
- |
address of an integer to store the number of characters processed |
base |
- |
the number base |
#include <iostream>
#include <string>
int main(){
std::string str1 = "45";
std::string str2 = "3.14159";
std::string str3 = "31337 with words";
std::string str4 = "words and 2";
int myint1 = std::stoi(str1);
int myint2 = std::stoi(str2);
int myint3 = std::stoi(str3);
// error: 'std::invalid_argument'
// int myint4 = std::stoi(str4);
std::cout << "std::stoi(\"" << str1 << "\") is " << myint1 << '\n';
std::cout << "std::stoi(\"" << str2 << "\") is " << myint2 << '\n';
std::cout << "std::stoi(\"" << str3 << "\") is " << myint3 << '\n';
//std::cout << "std::stoi(\"" << str4 << "\") is " << myint4 << '\n';
}
string转无符号型long:
unsigned long stoul( const std::string& str, std::size_t* pos = 0, int base = 10 );
unsigned long stoul( const std::wstring& str, std::size_t* pos = 0, int base = 10 );
unsigned long long stoull( const std::string& str, std::size_t* pos = 0, int base = 10 );
unsigned long long stoull( const std::wstring& str, std::size_t* pos = 0, int base = 10 );
str |
- |
the string to convert |
pos |
- |
address of an integer to store the number of characters processed |
base |
- |
the number base |
string转浮点型:
float stof( const std::string& str, std::size_t* pos = 0 );
float stof( const std::wstring& str, std::size_t* pos = 0 );
double stod( const std::string& str, std::size_t* pos = 0 );
double stod( const std::wstring& str, std::size_t* pos = 0 );
long double stold( const std::string& str, std::size_t* pos = 0 );
long double stold( const std::wstring& str, std::size_t* pos = 0 );
str |
- |
the string to convert |
pos |
- |
address of an integer to store the number of characters processed |
各个类型转string:
Defined in header <string>
std::string to_string( int value );
std::string to_string( long value );
std::string to_string( long long value );
std::string to_string( unsigned value );
std::string to_string( unsigned long value );
std::string to_string( unsigned long long value );
std::string to_string( float value );
std::string to_string( double value );
std::string to_string( long double value );
#include <iostream>
#include <string>
int main() {
double f = 23.43;
double f2 = 1e-9;
double f3 = 1e40;
double f4 = 1e-40;
double f5 = 123456789;
std::string f_str = std::to_string(f);
std::string f_str2 = std::to_string(f2); // Note: returns "0.000000"
std::string f_str3 = std::to_string(f3); // Note: Does not return "1e+40".
std::string f_str4 = std::to_string(f4); // Note: returns "0.000000"
std::string f_str5 = std::to_string(f5);
std::cout << "std::cout: " << f << '\n'
<< "to_string: " << f_str << "\n\n"
<< "std::cout: " << f2 << '\n'
<< "to_string: " << f_str2 << "\n\n"
<< "std::cout: " << f3 << '\n'
<< "to_string: " << f_str3 << "\n\n"
<< "std::cout: " << f4 << '\n'
<< "to_string: " << f_str4 << "\n\n"
<< "std::cout: " << f5 << '\n'
<< "to_string: " << f_str5 << '\n';
}
将字节字符串转换为整数值:
long strtol( const char *str, char **str_end, int base );
long long strtoll( const char *str, char **str_end, int base );
str |
- |
pointer to the null-terminated byte string to be interpreted |
str_end |
- |
pointer to a pointer to character. |
base |
- |
base of the interpreted integer value |
#include <iostream>
#include <string>
#include <cerrno>
#include <cstdlib>
int main()
{
const char* p = "10 200000000000000000000000000000 30 -40";
char *end;
std::cout << "Parsing '" << p << "':\n";
for (long i = std::strtol(p, &end, 10);
p != end;
i = std::strtol(p, &end, 10))
{
std::cout << "'" << std::string(p, end-p) << "' -> ";
p = end;
if (errno == ERANGE){
std::cout << "range error, got ";
errno = 0;
}
std::cout << i << '\n';
}
}
将字节字符串转换为浮点型
float strtof( const char* str, char** str_end );
double strtod( const char* str, char** str_end );
long double strtold( const char* str, char** str_end );
str |
- |
pointer to the null-terminated byte string to be interpreted |
str_end |
- |
pointer to a pointer to character. |
#include <iostream>
#include <string>
#include <cerrno>
#include <cstdlib>
int main()
{
const char* p = "111.11 -2.22 0X1.BC70A3D70A3D7P+6 1.18973e+4932zzz";
char* end;
std::cout << "Parsing \"" << p << "\":\n";
for (double f = std::strtod(p, &end); p != end; f = std::strtod(p, &end))
{
std::cout << "'" << std::string(p, end-p) << "' -> ";
p = end;
if (errno == ERANGE){
std::cout << "range error, got ";
errno = 0;
}
std::cout << f << '\n';
}
}
一个非常好的网站: http://en.cppreference.com/w/cpp/string/basic_string/stol