Julia是否提供字符串'contains'子串方法？如何检测子串并获取其索引？

Hey there! Let's tackle your Julia string questions one by one:

1. Does Julia have a 'contains' method for substring checks? #

Absolutely! Julia comes with a built-in contains() function that’s perfect for checking if a substring exists in a target string. It returns a boolean (true if the substring is found, false otherwise).

Fun fact: contains() is actually an alias for occursin()—you can use either interchangeably, depending on which reads more naturally to you.

Here’s a quick example:

my_string = "I love coding in Julia!"
substring = "Julia"

contains(my_string, substring)  # Returns true
occursin("Python", my_string)   # Returns false (same functionality as contains)

2. How to detect a substring and get its occurrence index in Julia? #

If you need to not just check for existence but also get the position(s) of the substring, Julia has several handy functions for this:

Get the first occurrence index #

Use findfirst() to retrieve the range (start and end indices) of the first match. If the substring isn’t found, it returns nothing, so always handle that case to avoid errors.

Example:

text = "Julia is great—Julia is flexible!"
target_sub = "Julia"

first_match = findfirst(target_sub, text)
if first_match !== nothing
    println("First match starts at index: ", first_match.start)
    println("First match ends at index: ", first_match.stop)
end
# Output:
# First match starts at index: 1
# First match ends at index: 5

Get all occurrence indices #

To find every place the substring appears, use findall(). It returns an array of ranges, one for each match.

Example:

all_matches = findall(target_sub, text)
for (i, match) in enumerate(all_matches)
    println("Match $i: starts at ", match.start, ", ends at ", match.stop)
end
# Output:
# Match 1: starts at 1, ends at 5
# Match 2: starts at 17, ends at 21

Find the next occurrence after a specific position #

If you want to search starting from a particular index (e.g., after the first match), use findnext():

# Start searching from index 6 (right after the first "Julia")
second_match = findnext(target_sub, text, 6)
println("Second match starts at: ", second_match.start)  # Output: 17

内容的提问来源于stack exchange，提问作者logankilpatrick