Removing trailing newline character from fgets input

Question

I am trying to get some data from the user and send it to another function in gcc  The code is something like this   printf  Enter your Name      if    fgets Name  sizeof Name  stdin     NULL         fprintf stderr   Error reading Name  n        exit 1       However  I find that it has a newline  n character in the end  So if I enter John it ends up sending John n  How do I remove that  n and send a proper string

User · Answer

The steps to remove the newline character in the perhaps most obvious way:

Determine the length of the string inside NAME by using strlen(), header string.h. Note that strlen() does not count the terminating \0.

size_t sl = strlen(NAME);

Look if the string begins with or only includes one \0 character (empty string). In this case sl would be 0 since strlen() as I said above doesn´t count the \0 and stops at the first occurrence of it:

if(sl == 0)
{
   // Skip the newline replacement process.
}

Check if the last character of the proper string is a newline character '\n'. If this is the case, replace \n with a \0. Note that index counts start at 0 so we will need to do NAME[sl - 1]:

if(NAME[sl - 1] == '\n')
{
   NAME[sl - 1] = '\0';
}

Note if you only pressed Enter at the fgets() string request (the string content was only consisted of a newline character) the string in NAME will be an empty string thereafter.

We can combine step 2. and 3. together in just one if-statement by using the logic operator &&:

if(sl > 0 && NAME[sl - 1] == '\n')
{
   NAME[sl - 1] = '\0';
}

The finished code:

size_t sl = strlen(NAME);
if(sl > 0 && NAME[sl - 1] == '\n')
{
   NAME[sl - 1] = '\0';
}

If you rather like a function for use this technique by handling fgets output strings in general without retyping each and every time, here is fgets_newline_kill:

void fgets_newline_kill(char a[])
{
    size_t sl = strlen(a);

    if(sl > 0 && a[sl - 1] == '\n')
    {
       a[sl - 1] = '\0';
    }
}

In your provided example, it would be:

printf("Enter your Name: ");

if (fgets(Name, sizeof Name, stdin) == NULL) {
    fprintf(stderr, "Error reading Name.\n");
    exit(1);
}
else {
    fgets_newline_kill(NAME);
}

Note that this method does not work if the input string has embedded \0s in it. If that would be the case strlen() would only return the amount of characters until the first \0. But this isn´t quite a common approach, since the most string-reading functions usually stop at the first \0 and take the string until that null character.

Aside from the question on its own. Try to avoid double negations that make your code unclearer: if (!(fgets(Name, sizeof Name, stdin) != NULL) {}. You can simply do if (fgets(Name, sizeof Name, stdin) == NULL) {}.

User · Answer

The function below is a part of string processing library I am maintaining on Github  It removes and unwanted characters from a string  exactly what you want  int zstring search chr const char  token char s       if   token    s    0           return 0       for    token  token            if   token    s              return 1       return 0     char  zstring remove chr char  str const char  bad        char  src   str    dst   str      while  src          if zstring search chr bad  src               src            else              dst      src        assign first  then incement          dst   0           return str      An example usage could be   Example Usage       char s    this is a trial string to test the function          char const  d             printf   s n  zstring remove chr s d       Example Output       thisisatrialstringtotestthefunction   You may want to check other available functions  or even contribute to the project    https   github com fnoyanisi zString

User · Answer

For single   n  trimming   void remove new line char  string        size t length   strlen string       if  length  gt  0   amp  amp   string length-1       n                  string length-1     0             for multiple   n  trimming   void remove multi new line char  string      size t length   strlen string     while  length gt 0   amp  amp   string length-1       n              --length        string length     0

User · Answer

Direct to remove the   n  from the fgets output if every line has   n   line strlen line  - 1      0     Otherwise   void remove newline ch char  line        int new line   strlen line  -1      if  line new line       n           line new line      0

User · Answer

Below is a fast approach to remove a potential   n  from a string saved by fgets    It uses strlen    with 2 tests   char buffer 100   if  fgets buffer  sizeof buffer  stdin     NULL       size t len   strlen buffer     if  len  gt  0  amp  amp  buffer len-1       n         buffer --len      0         Now use buffer and len as needed   This method has the side benefit of a len value for subsequent code   It can be easily faster than strchr Name    n     Ref  YMMV  but both methods work     buffer  from the original fgets   will not contain in   n  under some circumstances  A  The line was too long for buffer so only char preceding the   n  is saved in buffer  The unread characters remain in the stream  B  The last line in the file did not end with a   n      If input has embedded null characters   0  in it somewhere  the length reported by strlen   will not include the   n  location     Some other answers  issues     strtok buffer    n    fails to remove the   n  when buffer is   n    From this answer - amended after this answer to warn of this limitation   The following fails on rare occasions when the first char read by fgets   is   0    This happens when input begins with an embedded   0    Then buffer len -1  becomes buffer SIZE MAX  accessing memory certainly outside the legitimate range of buffer  Something a hacker may try or found in foolishly reading UTF16 text files   This was the state of an answer when this answer was written   Later a non-OP edited it to include code like this answer s check for      size t len   strlen buffer   if  buffer len - 1       n         FAILS when len    0   buffer len -1      0      sprintf buffer   s  buffer   is undefined behavior  Ref   Further  it does not save any leading  separating or trailing whitespace   Now deleted   Edit due to good later answer  There are no problems with the 1 liner buffer strcspn buffer    n      0  other than performance as compared to the strlen   approach   Performance in trimming is usually not an issue given code is doing I O - a black hole of CPU time   Should following code need the string s length or is highly performance conscious  use this strlen   approach   Else the strcspn   is a fine alternative

User · Answer

Tim Cas one liner is amazing for strings obtained by a call to fgets  because you know they contain a single newline at the end    If you are in a different context and want to handle strings that may contain more than one newline  you might be looking for strrspn  It is not POSIX  meaning you will not find it on all Unices  I wrote one for my own needs      Returns the length of the segment leading to the last     characters of s in accept     size t strrspn  const char  s  const char  accept      const char  ch    size t len   strlen s    more     if  len  gt  0        for  ch   accept    ch    0   ch            if  s len - 1      ch            len--          goto more                      return len      For those looking for a Perl chomp equivalent in C  I think this is it  chomp only removes the trailing newline    line strrspn string    r n      0    The strrcspn function      Returns the length of the segment leading to the last     character of reject in s     size t strrcspn  const char  s  const char  reject      const char  ch    size t len   strlen s     size t origlen   len     while  len  gt  0        for  ch   reject    ch    0   ch            if  s len - 1      ch            return len                    len--        return origlen

User · Answer

My Newbie way  -  Please let me know if that s correct  It seems to be working for all my cases    define IPT SIZE 5  int findNULL char  arr        for  int i   0  i  lt  strlen arr   i                  if    arr i       n                         return i                      return 0     int main         char  input   malloc IPT SIZE   1   sizeof char    buff      int counter   0         prompt user for the input      printf  input string no longer than  i characters     IPT SIZE       do               fgets input  1000  stdin             input   findNULL input       0           if  strlen input   gt  IPT SIZE                        printf  error  the given string is too large  try again    n                counter                        if the counter exceeds 3  exit the program  custom function           errorMsgExit counter  3              while  strlen input   gt  IPT SIZE      rest of the program follows  free input  return 0

User · Answer

If using getline is an option - Not neglecting its security issues and if you wish to brace pointers - you can avoid string functions as the getline returns the number of characters  Something like below  include  lt stdio h gt   include  lt stdlib h gt  int main         char  fname   lname      size t size   32  nchar     Max size of strings and number of characters read     fname   malloc size   sizeof  fname       lname   malloc size   sizeof  lname       if  NULL    fname    NULL    lname                printf  quot Error in memory allocation  quot            exit 1             printf  quot Enter first name  quot        nchar   getline  amp fname   amp size  stdin       if  nchar    -1     getline return -1 on failure to read a line                printf  quot Line couldn t be read   quot               This if block could be repeated for next getline too         exit 1             printf  quot Number of characters read   zu n quot   nchar       fname nchar - 1      0       printf  quot Enter last name  quot        nchar   getline  amp lname   amp size  stdin       printf  quot Number of characters read   zu n quot   nchar       lname nchar - 1      0       printf  quot Name entered  s  s n quot   fname  lname       return 0     Note  The   security issues   with getline shouldn t be neglected though

User · Answer

The elegant way  Name strcspn Name   quot  n quot      0   The slightly ugly way  char  pos  if   pos strchr Name    n       NULL       pos     0   else        input too long for buffer  flag error     The slightly strange way  strtok Name   quot  n quot     Note that the strtok function doesn t work as expected if the user enters an empty string  i e  presses only Enter   It leaves the  n character intact  There are others as well  of course

User · Answer

I m a bit surprised that no one has mentioned this   In general  rather than trimming data that you don t want  avoid writing it in the first place   If you don t want the newline in the buffer  don t use fgets   Instead  use getc or fgetc or scanf   Perhaps something like   include  lt stdio h gt   include  lt stdlib h gt  int main void            char Name 256           char fmt 32           int rc          sprintf fmt   quot    zd   n  quot   sizeof Name - 1           if   rc   scanf fmt  Name      1                     printf  quot Name    s n quot   Name                     return rc    1   EXIT SUCCESS   EXIT FAILURE

User · Answer

size t ln   strlen name  - 1  if   name  amp  amp  name ln       n        name ln      0

User · Answer

Perhaps the simplest solution uses one of my favorite little-known functions  strcspn     buffer strcspn buffer    n      0    If you want it to also handle   r   say  if the stream is binary    buffer strcspn buffer    r n      0     works for LF  CR  CRLF  LFCR        The function counts the number of characters until it hits a   r  or a   n   in other words  it finds the first   r  or   n    If it doesn t hit anything  it stops at the   0   returning the length of the string    Note that this works fine even if there is no newline  because strcspn stops at a   0   In that case  the entire line is simply replacing   0  with   0

User · Answer

for int i   0  i  lt  strlen Name   i           if Name i       n   Name i      0       You should give it a try  This code basically loop through the string until it finds the   n   When it s found the   n  will be replaced by the null character terminator   0   Note that you are comparing characters and not strings in this line  then there s no need to use strcmp     if Name i       n   Name i      0     since you will be using single quotes and not double quotes  Here s a link about single vs double quotes if you want to know more

[c] Removing trailing newline character from fgets() input

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