Strings in C how to get subString

Question

I have a string   char   someString    If I want the first five letters of this string and want to set it to otherString  how would I do it

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You ll need to allocate memory for the new string otherString  In general for a substring of length n  something like this may work for you  don t forget to do bounds checking      char  subString char  someString  int n        char  new   malloc sizeof char  n 1      strncpy new  someString  n      new n      0      return new      This will return a substring of the first n characters of someString  Make sure you free the memory when you are done with it using free

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char  someString    abcdedgh   char  otherString   0   otherString    char  malloc 5 1   memcpy otherString someString 5   otherString 5    0    UPDATE  Tip  A good way to understand definitions is called the right-left rule  some links at the end    Start reading from identifier and say aloud     someString is     Now go to right of someString  statement has ended with a semicolon  nothing to say   Now go left of identifier    is encountered     so say     a pointer to      Now go to left of      the keyword char is found     say    char   Done   So char  someString      someString is a pointer to char    Since a pointer simply points to a certain memory address  it can also be used as the  starting point  for an  array  of characters   That works with anything    give it a go   char  s 2       gt  s is an array of two pointers to char char   someThing      gt  someThing is a pointer to a pointer to char    Note  We look in the brackets first  and then move outward char    s  2       gt  s is a pointer to an array of two char   Some links  How to interpret complex C C   declarations and  How To Read C Declarations

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Generalized   char  subString  const char  input  int offset  int len  char  dest      int input len   strlen  input      if  offset   len  gt  input len           return NULL         strncpy  dest  input   offset  len     return dest     char dest 80   const char  source    hello world    if  subString  source  0  5  dest       printf    s n   dest

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include  lt stdio h gt   include  lt string h gt   int main              char someString    abcdedgh           char otherString    00000           memcpy  otherString  someString  5           printf   someString   s notherString   s n   someString  otherString           return 0      You will not need stdio h if you don t use the printf statement and putting constants in all but the smallest programs is bad form and should be avoided

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This code is substr function that mimics function of same name present in other languages  just parse  string  start and number of characters like    include  lt stdio h gt   printf   SUBSTR   s   substr  HELLO WORLD   2 5       The above will print HELLO  If you pass a value over the string length  it will be silently ignored  as the loop only iterates the length of the string    include  lt stdlib h gt   char  substr char  s  int a  int b        char  r    char  malloc b       strcpy r           int m 0  n 0      while s n     0                 if   n gt  a  amp  amp  m lt b                r m    s n               m                         n              r m    0       return r

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I think it s easy way    but I don t know how I can pass the result variable directly then I create a local char array as temp and return it   char  substr char  buff  uint8 t start uint8 t len  char  substr        strncpy substr  buff start  len       substr len    0      return substr

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You can treat C strings like pointers  So when you declare   char str 10     str can be used as a pointer  So if you want to copy just a portion of the string you can use   char str1 24     This is a simple string    char str2 6   strncpy str1   10  str2 6     This will copy 6 characters from the str1 array into str2 starting at the 11th element

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char largeSrt      123456789-123       original string  char   substr  substr   strchr largeSrt   -           we save the new string  -123  int substringLength   strlen largeSrt  - strlen substr      13-4 9  bigger string size  -  new string size    char  newStr   malloc sizeof char    substringLength   1     keep memory free to new string strcpy newStr  largeSrt  substringLength       copy only 9 characters  newStr substringLength      0      close the new string with final character  printf  newStr  s n   newStr    free newStr        you free the memory

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You can use snprintf to get a substring of a char array with precision  Here is a file example called  substring c     include  lt stdio h gt   int main         const char source      This is a string array       char dest 17           get first 16 characters using precision     snprintf dest  sizeof dest      16s   source           print substring     puts dest        end main   Output      This is a string   Note   For further information see printf man page

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include  lt string h gt      char otherString 6      note 6  not 5  there s one there for the null terminator     strncpy otherString  someString  5   otherString 5      0      place the null terminator

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strncpy otherString  someString  5     Don t forget to allocate memory for otherString

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Doing it all in two fell swoops   char  otherString   strncpy  char  malloc 6   someString   otherString 5    0

[c] Strings in C, how to get subString

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