How does strtok work c

Another possibility is to provide your own implementation of strtok that does not modify the initial arguments. The Linux Programmer's Manual man page on strtok 3 [ Linux ] states:. Never use this function. This function modifies its first argument. The identity of the delimiting character is lost. This function cannot be used on constant strings. The improper use of strtok is likely to result in truncated data, producing unexpected results later in program execution.

Search for vulnerabilities resulting from the violation of this rule on the CERT website. Answer 1: A string passed to strtok is no longer safe, as strtok modifies it.

Theoretically you should never refer to a string after passing it to strtok. The CCE accomplishes this by giving strtok a copy of the string and then freeing the copy.

Whoops, the CS isn't actually freeing the copy A fully rigorous solution would do sophisticated data flow analysis on the pointed-to strings Even if the code does the right thing, it may still be considered a mistake and 'fixed' by a future maintainer, which can lead to vuls later on Ok, so it's not too strict too say that the only valid use for a string after getting passed to strtok is as an argument to strcpy , memcpy , free , or as the lhs to an assignment?

Because strcpy is safe in this instance, as the destination string 's memory is allocated to be large enough to hold it. A null pointer is returned if the string cannot be split. The following piece of code will just split up the Hello world string in two and will return the first token extracted from the function.

To find all possible splits of the string, based on a given delimiter, the function needs to be called in a loop. See the example below to see how this works. Learn C from Scratch. Coderust: Hacking the Coding Interview.

View all Courses. All rights reserved. Courses Pricing. Splitting a string using strtok in C. Active Oldest Votes. Improve this answer. Floris Floris Sean Sean Andy Thomas Andy Thomas Most modern runtimes store the state in thread local storage. Which means that it is thread safe but not safe when used re-entrantly. Thanks for the correction. JuanR JuanR 5, 17 17 silver badges 28 28 bronze badges. The Overflow Blog. Does ES6 make JavaScript frameworks obsolete? Podcast Do polyglots have an edge when it comes to mastering programming Featured on Meta.

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