Defined in header <cstdlib> | ||
---|---|---|
int atoi( const char* str ); | (1) | |
long atol( const char* str ); | (2) | |
long long atoll( const char* str ); | (3) | (since C++11) |
Interprets an integer value in a byte string pointed to by str
. The implied radix is always 10.
Discards any whitespace characters until the first non-whitespace character is found, then takes as many characters as possible to form a valid integer number representation and converts them to an integer value. The valid integer value consists of the following parts:
If the value of the result cannot be represented, i.e. the converted value falls out of range of the corresponding return type, the behavior is undefined.
str | - | pointer to the null-terminated byte string to be interpreted |
Integer value corresponding to the contents of str
on success.
If no conversion can be performed, 0
is returned.
Actual C++ library implementations fall back to C library implementations of atoi
, atoil
, and atoll
, which either implement it directly (as in MUSL libc) or delegate to strtol
/strtoll
(as in GNU libc).
#include <cstdlib> #include <iostream> int main() { const auto data = { "42", "0x2A", // treated as "0" and junk "x2A", not as hexadecimal "3.14159", "31337 with words", "words and 2", "-012345", "10000000000" // note: out of int32_t range }; for (const char* s : data) { const int i{std::atoi(s)}; std::cout << "std::atoi('" << s << "') is " << i << '\n'; if (const long long ll{std::atoll(s)}; i != ll) std::cout << "std::atoll('" << s << "') is " << ll << '\n'; } }
Possible output:
(C++11)(C++11)(C++11) | converts a string to a signed integer (function) |
(C++11)(C++11) | converts a string to an unsigned integer (function) |
(C++11) | converts a byte string to an integer value (function) |
(C++11) | converts a byte string to an unsigned integer value (function) |
(C++11)(C++11) | converts a byte string to std::intmax_t or std::uintmax_t (function) |
(C++17) | converts a character sequence to an integer or floating-point value (function) |
C documentation for atoi, atol, atoll |
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