Check if a string contains a string in C

Question

I have a variable of type std  string   I want to check if it contains a certain std  string   How would I do that   Is there a function that returns true if the string is found  and false if it isn t

User · Answer

Actually  you can try to use boost library I think std  string doesn t supply enough method to do all the common string operation In boost you can just use the boost  algorithm  contains    include  lt string gt   include  lt boost algorithm string hpp gt   int main         std  string s  gengjiawen        std  string t  geng        bool b   boost  algorithm  contains s  t       std  cout  lt  lt  b  lt  lt  std  endl      return 0

User · Answer

Use std  string  find as follows   if  s1 find s2     std  string  npos        std  cout  lt  lt   found    lt  lt    n       Note   found   will be printed if s2 is a substring of s1  both s1 and s2 are of type std  string

User · Answer

You can try this  string s1    Hello   string s2    el   if strstr s1 c str   s2 c str          cout  lt  lt    S1 Contains S2

User · Answer

We can use this method instead  Just an example from my projects  Refer the code  Some extras are also included   Look to the if statements      Every C   program should have an entry point  Usually  this is the main function  Every C   Statement ends with a      semi-colon  But  pre-processor statements do not have    s at end  Also  every console program can be ended using  cin get     statement  so that the console won t exit instantly       include  lt string gt   include  lt bits stdc   h gt    Can Use instead of iostream  Also should be included to use the transform function   using namespace std  int main      The main function  This runs first in every program       string input       while input   exit            cin gt  gt input          transform input begin   input end   input begin     tolower     Converts to lowercase           if input find  name      std  string  npos     Gets a boolean value regarding the availability of the said text              cout lt  lt  My Name is AI  n                      if input find  age      std  string  npos               cout lt  lt  My Age is 2 minutes  n

User · Answer

If the size of strings is relatively big  hundreds of bytes or more  and c  17 is available  you might want to use Boyer-Moore-Horspool searcher  example from cppreference com     include  lt iostream gt   include  lt string gt   include  lt algorithm gt   include  lt functional gt   int main         std  string in    Lorem ipsum dolor sit amet  consectetur adipiscing elit                          sed do eiusmod tempor incididunt ut labore et dolore magna aliqua       std  string needle    pisci       auto it   std  search in begin    in end                       std  boyer moore searcher                         needle begin    needle end          if it    in end            std  cout  lt  lt   The string    lt  lt  needle  lt  lt    found at offset                      lt  lt  it - in begin    lt  lt    n       else         std  cout  lt  lt   The string    lt  lt  needle  lt  lt    not found n

User · Answer

include  lt algorithm gt            std  search  include  lt string gt  using std  search  using std  count  using std  string   int main         string mystring    The needle in the haystack       string str    needle       string  const iterator it      it   search mystring begin    mystring end                     str begin    str end       mystring end            if string is found    returns iterator to str s first element in mystring        if string is not found    returns iterator to mystring end    if  it    mystring end           string is found else        not found  return 0

User · Answer

You can try using the find function   string str   There are two needles in this haystack     string str2   needle     if  str find str2     string  npos         found

User · Answer

In the event if the functionality is critical to your system  it is actually beneficial to use an old strstr method  The std  search method within algorithm is the slowest possible  My guess would be that it takes a lot of time to create those iterators   The code that i used to time the whole thing is   include  lt string gt   include  lt cstring gt   include  lt iostream gt   include  lt algorithm gt   include  lt random gt   include  lt chrono gt   std  string randomString  size t len     int main int argc  char  argv              using namespace std  chrono           const size t haystacksCount   200000          std  string haystacks haystacksCount           std  string needle    hello            bool sink   true           high resolution clock  time point start  end          duration lt double gt  timespan           int sizes 10      10  20  40  80  160  320  640  1280  5120  10240             for int s 0  s lt 10    s                            std  cout  lt  lt  std  endl  lt  lt   Generating    lt  lt  haystacksCount  lt  lt    random haystacks of size    lt  lt  sizes s   lt  lt  std  endl                  for size t i 0  i lt haystacksCount    i                                            haystacks i    randomString sizes s                                       std  cout  lt  lt   Starting std  string find approach   lt  lt  std  endl                  start   high resolution clock  now                    for size t i 0  i lt haystacksCount    i                                            if haystacks i  find needle     std  string  npos                                                            sink    sink     useless action                                                             end   high resolution clock  now                    timespan   duration cast lt duration lt double gt  gt  end-start                   std  cout  lt  lt   Processing of    lt  lt  haystacksCount  lt  lt    elements took    lt  lt  timespan count    lt  lt    seconds    lt  lt  std  endl                   std  cout  lt  lt   Starting strstr approach   lt  lt  std  endl                  start   high resolution clock  now                    for size t i 0  i lt haystacksCount    i                                            if strstr haystacks i  c str    needle c str                                                               sink    sink     useless action                                                             end   high resolution clock  now                    timespan   duration cast lt duration lt double gt  gt  end-start                   std  cout  lt  lt   Processing of    lt  lt  haystacksCount  lt  lt    elements took    lt  lt  timespan count    lt  lt    seconds    lt  lt  std  endl                   std  cout  lt  lt   Starting std  search approach   lt  lt  std  endl                  start   high resolution clock  now                    for size t i 0  i lt haystacksCount    i                                            if std  search haystacks i  begin    haystacks i  end    needle begin    needle end       haystacks i  end                                                              sink    sink     useless action                                                             end   high resolution clock  now                    timespan   duration cast lt duration lt double gt  gt  end-start                   std  cout  lt  lt   Processing of    lt  lt  haystacksCount  lt  lt    elements took    lt  lt  timespan count    lt  lt    seconds    lt  lt  std  endl                     return 0     std  string randomString  size t len            static const char charset      abcdefghijklmnopqrstuvwxyz           static const int charsetLen   sizeof charset  - 1          static std  default random engine rng std  random device               static std  uniform int distribution lt  gt  dist 0  charsetLen           auto randChar    charset   amp dist   amp rng    - gt  char                           return charset  dist rng                         std  string result len  0           std  generate n result begin    len  randChar           return result      Here i generate random haystacks and search in them the needle  The haystack count is set  but the length of strings within each haystack is increased from 10 in the beginning to 10240 in the end  Most of the time the program spends actually generating random strings  but that is to be expected   The output is   Generating 200000 random haystacks of size 10 Starting std  string find approach Processing of 200000 elements took 0 00358503 seconds  Starting strstr approach Processing of 200000 elements took 0 0022727 seconds  Starting std  search approach Processing of 200000 elements took 0 0346258 seconds   Generating 200000 random haystacks of size 20 Starting std  string find approach Processing of 200000 elements took 0 00480959 seconds  Starting strstr approach Processing of 200000 elements took 0 00236199 seconds  Starting std  search approach Processing of 200000 elements took 0 0586416 seconds   Generating 200000 random haystacks of size 40 Starting std  string find approach Processing of 200000 elements took 0 0082571 seconds  Starting strstr approach Processing of 200000 elements took 0 00341435 seconds  Starting std  search approach Processing of 200000 elements took 0 0952996 seconds   Generating 200000 random haystacks of size 80 Starting std  string find approach Processing of 200000 elements took 0 0148288 seconds  Starting strstr approach Processing of 200000 elements took 0 00399263 seconds  Starting std  search approach Processing of 200000 elements took 0 175945 seconds   Generating 200000 random haystacks of size 160 Starting std  string find approach Processing of 200000 elements took 0 0293496 seconds  Starting strstr approach Processing of 200000 elements took 0 00504251 seconds  Starting std  search approach Processing of 200000 elements took 0 343452 seconds   Generating 200000 random haystacks of size 320 Starting std  string find approach Processing of 200000 elements took 0 0522893 seconds  Starting strstr approach Processing of 200000 elements took 0 00850485 seconds  Starting std  search approach Processing of 200000 elements took 0 64133 seconds   Generating 200000 random haystacks of size 640 Starting std  string find approach Processing of 200000 elements took 0 102082 seconds  Starting strstr approach Processing of 200000 elements took 0 00925799 seconds  Starting std  search approach Processing of 200000 elements took 1 26321 seconds   Generating 200000 random haystacks of size 1280 Starting std  string find approach Processing of 200000 elements took 0 208057 seconds  Starting strstr approach Processing of 200000 elements took 0 0105039 seconds  Starting std  search approach Processing of 200000 elements took 2 57404 seconds   Generating 200000 random haystacks of size 5120 Starting std  string find approach Processing of 200000 elements took 0 798496 seconds  Starting strstr approach Processing of 200000 elements took 0 0137969 seconds  Starting std  search approach Processing of 200000 elements took 10 3573 seconds   Generating 200000 random haystacks of size 10240 Starting std  string find approach Processing of 200000 elements took 1 58171 seconds  Starting strstr approach Processing of 200000 elements took 0 0143111 seconds  Starting std  search approach Processing of 200000 elements took 20 4163 seconds

User · Answer

From so many answers in this website I didn t find out a clear answer so in 5-10 minutes I figured it out the answer myself  But this can be done in two cases    Either you KNOW the position of the sub-string you search for in the string Either you don t know the position and search for it  char by char      So  let s assume we search for the substring  cd  in the string  abcde   and we use the simplest substr built-in function in C     for 1    include  lt iostream gt   include  lt string gt       using namespace std  int i   int main         string a    abcde       string b   a substr 2 2         2 will be c  Why  because we start counting from 0 in a string  not from 1       cout  lt  lt   substring of a is     lt  lt  b  lt  lt  endl      return 0      for 2    include  lt iostream gt   include  lt string gt   using namespace std  int i   int main         string a    abcde        for  i 0 i lt a length    i                  if  a substr i 2      cd                     cout  lt  lt   substring of a is     lt  lt  a substr i 2   lt  lt  endl        i will iterate from 0 to 5 and will display the substring only when the condition is fullfilled                      return 0

User · Answer

This is a simple function  bool find string line  string sWord        bool flag   false      int index   0  i  helper   0      for  i   0  i  lt  line size    i                  if  sWord at index     line at i                         if  flag    false                                flag   true                  helper   i                            index                      else                       flag   false              index   0                    if  index    sWord size                          break                      if   i 1-helper     index                return true            return false

User · Answer

Starting from C  23 you can use std  string  contains  include  lt string gt   const auto haystack   std  string  quot haystack with needles quot    const auto needle   std  string  quot needle quot     if  haystack contains needle            found

User · Answer

If you don t want to use standard library functions  below is one solution    include  lt iostream gt   include  lt string gt   bool CheckSubstring std  string firstString  std  string secondString       if secondString size    gt  firstString size            return false       for  int i   0  i  lt  firstString size    i             int j   0             If the first characters match         if firstString i     secondString j                int k   i              while  firstString i     secondString j   amp  amp  j  lt  secondString size                     j                    i                              if  j    secondString size                    return true              else    Re-initialize i to its original value                 i   k                      return false     int main        std  string firstString  secondString       std  cout  lt  lt   Enter first string        std  getline std  cin  firstString        std  cout  lt  lt   Enter second string        std  getline std  cin  secondString        if CheckSubstring firstString  secondString           std  cout  lt  lt   Second string is a substring of the frist string  n       else         std  cout  lt  lt   Second string is not a substring of the first string  n        return 0

User · Answer

You can also use the System namespace  Then you can use the contains method    include  lt iostream gt  using namespace System   int main        String   wholeString    My name is Malindu        if wholeString- gt ToLower  - gt Contains  malindu             std  cout lt  lt  Found             else          std  cout lt  lt  Not Found

[c++] Check if a string contains a string in C++

Examples related to c++

Examples related to string

Examples related to substring