Hello again,
I am trying to strip first 4 characters from a string, and put the result in a variable buf. this is basically what I have now:
I keep getting seg fualt. I have tried it other ways but then I get garbage characters or FFFFF.Code:#include <stdio.h> #include <string.h> int main(void) { char buf[10]; char temp[10]; int c; printf("enter string>"); fgets(temp,10,stdin); for (c=0;c<5;c++) { strcpy(buf,temp[c]); } }
Any help is appreciated as always.
Thanks.
Brad
Try using strncpy instead of strcpy. That way you can specify how many characters to copy:
Code:#include <stdio.h> #include <string.h> int main(void) { char buf[10]; char temp[10]; int c; printf("enter string>"); fgets(temp,10,stdin); strncpy( buf, temp, 4 ); buf[4] = '\0'; puts( buf ); }
thanks Noir.
I tried your suggestion, but I need to do it in a loop. Lets say i type hello. I just wan to strip out hell and put it into buf. does that make sense?
p.s. sorry to start a huge ordeal on scanf.
EDIT: Whoops, I misinterpretted you. I though you wanted to strip off the first four characters and place the rest in buf. But you meant that you only want to KEEP the first four. Noir's code is correct for that.Code:#include <stdio.h> #include <string.h> int main(void) { char buf[10]; char temp[10]; int c; printf("enter string>"); fflush(stdout); fgets(temp,10,stdin); buf[0] = '\0'; if(strlen(temp) > 4) { strcpy(buf, temp + 4); } }
But notice the call to fflush(). You need that because there is no newline on the preceding printf(). Which means the stdout buffer might not flush, and you might not see the string. So, you must flush the buffer yourself.
Last edited by brewbuck; 04-20-2007 at 02:14 PM.
Not from where I'm sitting. If you copy 4 characters from temp into buf, then if temp has "hello", buf will have "hell" after calling strncpy(). If you also want to remove those characters from temp, you need to shift them away after copying them. You can do that with memmove:but I need to do it in a loop
or with a loop:Code:strncpy( buf, temp, 4 ); buf[4] = '\0'; memmove( temp, temp + 4, strlen( temp + 4 ) );
Code:strncpy( buf, temp, 4 ); buf[4] = '\0'; for ( c = 0; temp[c]; c++ ) { temp[c] = temp[c + 1]; }No biggie. It was a good debate until the other guy started showing his true colors.p.s. sorry to start a huge ordeal on scanf.
for ( c = 0; temp[c]; c++ ) I have never seen for loop like this. The second part temp[c], I have always seen it with operator.(index<string)What does that mean?
The loop runs until the middle expression becomes false. temp[c] is just the c'th character of the string (counting from zero). The end of the string is terminated by a zero byte. The value zero is false. Therefore, this loop terminates when it reaches the end of the string.Originally Posted by bradleyd
great explanation, thanks.
never mind. I was goin to say the loop was cutting of the first character, but I figured it out.
A string is just an array of characters ending with a '\0':
In C, any non-zero value is true, and 0 is false. So tmp[0] is true, tmp[1] is true, etc. all the way to tmp[5] which is false and would break the loop.Code:char tmp[] = { 'h', 'e', 'l', 'l', 'o', '\0' };
You could write your own strlen() function that just looked like this:
Code:int my_strlen(char *str) { int i = 0; while(str[i]) i++; return i; }
Last edited by itsme86; 04-20-2007 at 02:58 PM.
If you understand what you're doing, you're not learning anything.
Thanks for all your help, I understand it a little better now.
Take care.
