NAME¶

std::strtok - std::strtok

Synopsis¶

Defined in header <cstring>
char* strtok( char* str, const char* delim );

Finds the next token in a null-terminated byte string pointed to by str. The
separator characters are identified by null-terminated byte string pointed to by
delim.

This function is designed to be called multiple times to obtain successive tokens
from the same string.

* If str is not a null pointer, the call is treated as the first call to strtok
for this particular string. The function searches for the first character which
is not contained in delim.

* If no such character was found, there are no tokens in str at all, and the
function returns a null pointer.
* If such character was found, it is the beginning of the token. The function then
searches from that point on for the first character that is contained in delim.

* If no such character was found, str has only one token, and the future calls to
strtok will return a null pointer.
* If such character was found, it is replaced by the null character '\0' and the
pointer to the following character is stored in a static location for subsequent
invocations.
* The function then returns the pointer to the beginning of the token.
* If str is a null pointer, the call is treated as a subsequent call to strtok:
the function continues from where it left in previous invocation. The behavior
is the same as if the previously stored pointer is passed as str.

Parameters¶

str - pointer to the null-terminated byte string to tokenize
delim - pointer to the null-terminated byte string identifying delimiters

Return value¶

Pointer to the beginning of the next token or a nullptr if there are no more tokens.

Notes¶

This function is destructive: it writes the '\0' characters in the elements of the
string str. In particular, a string literal cannot be used as the first argument of
std::strtok.

Each call to this function modifies a static variable: is not thread safe.

Unlike most other tokenizers, the delimiters in std::strtok can be different for
each subsequent token, and can even depend on the contents of the previous tokens.

Possible implementation¶

char* strtok(char* str, const char* delim)
{
static char* buffer;

if (str != nullptr)
buffer = str;

buffer += std::strspn(buffer, delim);

if (*buffer == '\0')
return nullptr;

char* const tokenBegin = buffer;

buffer += std::strcspn(buffer, delim);

if (*buffer != '\0')
*buffer++ = '\0';

return tokenBegin;
}

Actual C++ library implementations of this function delegate to the C library, where
it may be implemented directly (as in MUSL libc), or in terms of its reentrant
version (as in GNU libc).

Example¶

// Run this code

#include <cstring>
#include <iomanip>
#include <iostream>

int main()
{
char input[] = "one + two * (three - four)!";
const char* delimiters = "! +- (*)";
char* token = std::strtok(input, delimiters);
while (token)
{
std::cout << std::quoted(token) << ' ';
token = std::strtok(nullptr, delimiters);
}

std::cout << "\nContents of the input string now:\n\"";
for (std::size_t n = 0; n < sizeof input; ++n)
{
if (const char c = input[n]; c != '\0')
std::cout << c;
else
std::cout << "\\0";
}
std::cout << "\"\n";
}

Output:¶

"one" "two" "three" "four"
Contents of the input string now:
"one\0+ two\0* (three\0- four\0!\0"

See also¶

finds the first location of any character from a set of
strpbrk separators
(function)
returns the length of the maximum initial segment that consists
strcspn of only the characters not found in another byte string
(function)
returns the length of the maximum initial segment that consists
strspn of only the characters found in another byte string
(function)
ranges::split_view a view over the subranges obtained from splitting another view
views::split using a delimiter
(C++20) (class template) (range adaptor object)
C documentation for
strtok