Comparing two strings, problems with strcmp

c strcmp strcpy
Barsan Ionut picture Barsan Ionut · Oct 20, 2013 · Viewed 14.8k times · Source

I'm trying to check if the line read from stdin begins with "login:" but strcmp does not seem to work.

char s1[20], s2[20];
fgets(s1, 20, stdin);
strncpy(s2,s1,6);
strcmp(s2, "login:");
if( strcmp(s2, "login:") == 0)
    printf("s2 = \"login:\"\n");
else
    printf("s2 != \"login:\"\n");

I don't care what comes after "login:", i just want to make sure that's how the command is given. What am i doing wrong?

Answer

Farouq Jouti picture Farouq Jouti · Oct 20, 2013

strcmp returns 0 if the two strings are exactly the same to accomplish what you want to do

Use :

strstr(s2 , "login:")

(It return NULL if the string doesn't exist in s2)

or

strncmp(s2 , "login:" , 6)

This will compare the first 6 characters (if s2 begins with "login:" , it will return 0)

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