Defined in header <cstring> | ||
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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.
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
. str
at all, and the function returns a null pointer. delim
. str
has only one token, and the future calls to strtok
will return a null pointer. '\0'
and the pointer to the following character is stored in a static location for subsequent invocations. 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
. str | - | pointer to the null-terminated byte string to tokenize |
delim | - | pointer to the null-terminated byte string identifying delimiters |
Pointer to the beginning of the next token or a nullptr
if there are no more tokens.
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.
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).
#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"
finds the first location of any character from a set of separators (function) |
|
returns the length of the maximum initial segment that consists of only the characters not found in another byte string (function) |
|
returns the length of the maximum initial segment that consists of only the characters found in another byte string (function) |
|
(C++20) | a view over the subranges obtained from splitting another view using a delimiter (class template) (range adaptor object) |
C documentation for strtok |
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