C + +. "Go" C + + numeric type and string conversion

1, C + + numeric type and string conversion-johngu-blog Park. HTML (https://www.cnblogs.com/johngu/p/7878029.html)

2.

1. Convert a numeric type to string1.1 using a function template +ostringstream

Use function templates to convert basic data types (integer, character, Real, Boolean) to String.

// ostringstream object is used for formatted output, commonly used to convert various types to string type // ostringstream only supports << operator template <typenameT> string toString (constT & t) {ostringstream oss; // Create a format The output stream oss << t; // Pass the value as returnoss.str ();} cout << toString (14.2) << endl; // Real-> string: Output 14.2cout << toString (12301 ) <endl; // integer-> string: output 12301cout << toString (123456789785) << endl; // long integer-> string: output 123456789785cout << toString (true) << endl; // boolean -> string: output 1

1.2 using standard library functions std::to_string ()

The STD command space has a C + + standard library function std::to_string () that can be used to convert a numeric type to a string. The Include header file is required for use<string>.

The function prototype is stated as follows:

string to_string (intval);string to_string (longval);string to_string (longlongval);string to_string (unsigned val);string to_string (unsigned longval);string to_string (unsigned longlongval);string to_string (floatval);string to_string (doubleval);string to_string (longdoubleval);

2.string conversion to numeric type 2.1 using function template + Istringstream

StringStream has been introduced in methods that convert int or float types to string types, and can also be used as a type of string to convert to a commonly used numeric type.

#include <iostream> #include <sstream> // The use of stringstream needs to include this header file usingnamespacestd; // Template function: convert string type variables to commonly used numeric types (this method has universal applicability) template <classType> Type stringToNum (conststring & str) {istringstream iss (str); Type num; iss >> num; returnnum;} intmain (intargc, char * argv []) {string str ("00801"); cout << stringToNum <int> (str ) << endl; system ("pause"); return0;}

2.2 Using C standard library functions

The practice is to first convert a string to a char* string, and then convert it to the desired numeric type by the appropriate type conversion function. You need to include standard library functions<stdlib.h>.
(1) string conversion to int32_t

string love = "77"; intilove = atoi (love.c_str ()); / or 16-bit platform converted to long intintilove = strtol (love.c_str (), NULL, 10);

(2) string conversion to uint32_t

// str: String to be converted // endptr: Point to the first non-numeric character after the number in str // base: Conversion base (base), ranging from 2 to 36 unsigned longintstrtoul (constchar * str, char ** endptr, intbase); #Example string love = "77"; unsigned longul; ul = strtoul (love.c_str (), NULL, 10);

(3) string conversion to uint64_t

string love="77";longlongllLove=atoll(love.c_str());

(4) string conversion to uint64_t

UNSIGNED long long int strtoull (const char* str, char** endptr, int base); #示例string love="all"UNSIGNED long long ull;ull = Strtoull (Love.c_str (), NULL, 0);

(5) string converted to float or double

string love="77.77";floatfLove=atof(love.c_str());doubledLove=atof(love.c_str());

(6) String conversion to long double

longdouble strtold (constchar* str, char** endptr);

2.3 using C + + standard library functions

Use the C + + library function introduced by c++11 to convert a string to a numeric type, and the corresponding library function is declared in the header file<string>.

name	prototypes	Description
Stoi	int stoi (const string& str, size_t* idx = 0, int base = 10); int stoi (const wstring& str, size_t* idx = 0, int base = 10);	Convert string to Integer (function template)
Stol	Long STOL (const string& str, size_t* idx = 0, int base = 10); Long STOL (const wstring& str, size_t* idx = 0, int base = 10);	Convert string to long int (function template)
Stoul	unsigned long Stoul (const string& str, size_t* idx = 0, int base = 10); unsigned long Stoul (const wstring& str, size_t* idx = 0, int base = 10);	Convert string to unsigned integer (function template)
Stoll	Long Long Stoll (const string& str, size_t* idx = 0, int base = 10); Long Long Stoll (const wstring& str, size_t* idx = 0, int base = 10);	Convert string to long long (function template)
Stoull	unsigned long long stoull (const string& str, size_t* idx = 0, int base = 10); unsigned long long stoull (const wstring& str, size_t* idx = 0, int base = 10);	Convert string to unsigned long long (function template)
Stof	Float Stof (const string& str, size_t* idx = 0); Float Stof (const wstring& str, size_t* idx = 0);	Convert string to float (function template)
Stod	Double stod (const string& str, size_t* idx = 0); Double stod (const wstring& str, size_t* idx = 0);	Convert string to double (function template)
Stold	Long double stold (const string& str, size_t* idx = 0); Long double stold (const wstring& str, size_t* idx = 0);	Convert string to long double (function template)

formal parameter description:
STR: The string and wstring versions are overloaded, representing the converted strings.

IDX: Represents a size_t* pointer type, which defaults to a null value. When not empty, the index of the first non-numeric character is obtained when the conversion succeeds. In general, because it is a direct char pointer that subtracts the address and start address values of the last non-numeric character, it also indicates the number of characters that were successfully converted, such as "10" to a value of 10 o'clock, which is*idx2.

Base: Represents the conversion datum, which is 10 binary by default.

Reference documents

[1] C + + Reference
[2]strtoul. C + + Reference
[2]strtoull. C + + Reference
[3]strtold. C + + Reference

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C + +. "Go" C + + numeric type and string conversion