---
name: "strtok_r"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/strtok_r"
---

# strtok\_r(3)

string tokenize reentrant

## NAME

strtok\_r - string tokenize reentrant

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <string.h>
```

**char \*strtok\_r(char \*\_Nullable restrict** *str***, const char \*restrict** *delim***,**                **char \*\*restrict** *saveptr***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**strtok\_r**():

```
    _POSIX_C_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
```

## DESCRIPTION

The **strtok\_r**() function is a reentrant version of [**strtok**(3)](/strtok/3.md).

The *saveptr* argument is a pointer to a *char \** variable that is used internally by **strtok\_r**() in order to maintain context between successive calls that parse the same string.

On the first call to **strtok\_r**(), *str* should point to the string to be parsed, and the value of *\*saveptr* is ignored (but see VERSIONS). In subsequent calls, *str* should be NULL, and *saveptr* (and the buffer that it points to) should be unchanged since the previous call.

Different strings may be parsed concurrently using sequences of calls to **strtok\_r**() that specify different *saveptr* arguments.

## RETURN VALUE

**strtok\_r**() returns a pointer to the next token, or NULL if there are no more tokens.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **strtok\_r**() | Thread safety | MT-Safe |

## VERSIONS

On some implementations, *\*saveptr* is required to be NULL on the first call to **strtok\_r**() that is being used to parse *str*.

## STANDARDS

POSIX.1-2008.

## HISTORY

POSIX.1-2001.

## EXAMPLES

The program below uses nested loops that employ **strtok\_r**() to break a string into a two-level hierarchy of tokens. The first command-line argument specifies the string to be parsed. The second argument specifies the delimiter byte(s) to be used to separate that string into "major" tokens. The third argument specifies the delimiter byte(s) to be used to separate the "major" tokens into subtokens.

An example of the output produced by this program is the following:

```
$ ./a.out 'a/bbb///cc;xxx:yyy:' ':;' '/'
1: a/bbb///cc
         --> a
         --> bbb
         --> cc
2: xxx
         --> xxx
3: yyy
         --> yyy
```

### Program source

```
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int
main(int argc, char *argv[])
{
    char *str1, *str2, *token, *subtoken;
    char *saveptr1, *saveptr2;
    int j;
    if (argc != 4) {
        fprintf(stderr, "Usage: %s string delim subdelim\n",
                argv[0]);
        exit(EXIT_FAILURE);
    }
    for (j = 1, str1 = argv[1]; ; j++, str1 = NULL) {
        token = strtok_r(str1, argv[2], &saveptr1);
        if (token == NULL)
            break;
        printf("%d: %s\n", j, token);
        for (str2 = token; ; str2 = NULL) {
            subtoken = strtok_r(str2, argv[3], &saveptr2);
            if (subtoken == NULL)
                break;
            printf("\t --> %s\n", subtoken);
        }
    }
    exit(EXIT_SUCCESS);
}
```

## SEE ALSO

[**strtok**(3)](/strtok/3.md)