C string from GetString() when strlen produces segmentation fault -

i running program in c. when run program segmentation fault error. in gdb when backtrace tells me

program received signal sigsegv, segmentation fault. __strlen_sse2_bsf () @ ../sysdeps/i386/i686/multiarch/strlen-sse2-bsf.s:51 51 movdqu (%edi), %xmm1

i believe has strlen.

the time use strlen is:

    string s = getstring();      int stringlength = strlen(s); 

when change strlen sizeof error stops.

what wrong code?

documentation of getstring

/*  * reads line of text standard input , returns   * string (char *), sans trailing newline character.  (ergo, if  * user inputs "\n", returns "" not null.)  returns null  * upon error or no input whatsoever (i.e., eof).  leading  * , trailing whitespace not ignored.  stores string on heap  * (via malloc); memory must freed caller avoid leak.  */  string getstring(void) {     // growable buffer chars     string buffer = null;      // capacity of buffer     unsigned int capacity = 0;      // number of chars in buffer     unsigned int n = 0;      // character read or eof     int c;      // iteratively chars standard input     while ((c = fgetc(stdin)) != '\n' && c != eof)     {         // grow buffer if necessary         if (n + 1 > capacity)         {             // determine new capacity: start @ 32 double             if (capacity == 0)                 capacity = 32;             else if (capacity <= (uint_max / 2))                 capacity *= 2;             else             {                 free(buffer);                 return null;             }              // extend buffer's capacity             string temp = realloc(buffer, capacity * sizeof(char));             if (temp == null)             {                 free(buffer);                 return null;             }             buffer = temp;         }          // append current character buffer         buffer[n++] = c;     }      // return null if user provided no input     if (n == 0 && c == eof)         return null;      // minimize buffer     string minimal = malloc((n + 1) * sizeof(char));     strncpy(minimal, buffer, n);     free(buffer);      // terminate string     minimal[n] = '\0';      // return string     return minimal; } 

the description of getstring() function states can return null on error or on eof.

if pass return value strlen() without checking, program crash.

string s = getstring(); int stringlength = 0;  if (s != 0)     stringlength = strlen(s); 

this @ least won't crash.

you might notice how confusion typedef char *string; causes , how little benefit confers, , take heart. don't have repeat mistakes of teaching you.

i observe code fragment:

// minimize buffer string minimal = malloc((n + 1) * sizeof(char)); strncpy(minimal, buffer, n); free(buffer); 

could better, , more simply, written as:

string minimal = realloc(buffer, n + 1); 

to shrink allocation correct size.