comparing value in array with string - c

Question

I have an array that looks like this:
char test[100]
then I want to compare whether or not this array has this specific sentence
if (test == "yup this is the sentence") {
// do stuff
}
Is this correct? Is there a better approach to this? Thank you.

Answer 1

You cannot do that in C. What you're doing here is checking identity equality (id est if your two pointers point the same memory zone).
What you can do is use libc strstr that does what you want :
#include <string.h>
if (strstr(test, "yup this is the sentence") != NULL)
{
// do stuff if test contains the sentence
}
Type man 3 strstr in a terminal to get more info about the function, and all its behaviours.
If you want to understand the behaviour of the function, here it is recoded in pure C, with one loop only :
char *strstr(const char *s1, const char *s2)
{
int begin;
int current;
begin = 0;
current = 0;
if (!*s2)
return ((char *)s1);
while (s1[begin])
{
if (s1[begin + current] == s2[current])
current++;
else
{
current = 0;
begin++;
}
if (!s2[current])
return ((char *)s1 + begin);
}
return (0);
}
It is part from a school project. The full project contains all the C library basic functions.
You can check out some other string manipulation functions here :
https://github.com/kube/libft/tree/master/src/strings

Answer 2

You could use strstr:
#include <stdio.h>
#include <stdlib.h>
#include<string.h>
int main(void) {
char test[256] = "This is a looooooonnnnggggg string which contains ('yup this is the sentence') my needed string inside";
if (strstr(test, "yup this is the sentence") != NULL){
printf("True\n");
}else{
printf("False\n");
}
return 0;
}
or you could use some pointer arithmetic:
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
void checkString(char *string1, char *string2);
int main(void){
char test[256] = "This is a looooooonnnnggggg string which contains ('yup this is the sentence') my needed string inside";
char string2[] = "yup this is the sentence";
checkString(test, string2);
return 0;
}
void checkString(char *string1, char *string2){
char *s1, *s2, *s3;
size_t lenstring1 = strlen(string1);
size_t lenstring2 = strlen(string2);
if (lenstring2 < 1){
printf("There is no substring found");
exit(1);
}
size_t i=0,j=0;
int found=0;
s1 = string1;
s2 = string2;
for(i = 0; i < lenstring1; i++){
if(*s1 == *s2){
s3 = s1;
for(j = 0;j < lenstring2;j++){
if(*s3 == *s2){
s3++;s2++;
}else{
break;
}
}
s2 = string2;
if(j == strlen(string2)){
found = 1;
printf("%s\nwas found at index : %zu\n",string2,i+1);
}
}
s1++;
}
if(found == 0){
printf("No match Found");
}
}
Output:
yup this is the sentence
was found at index : 53