Comparing two strings in C?

Question

This code is not working as the comparison is not being done. Why?

All names get past the if.

printf("Enter Product: \n");
scanf("%s", &nameIt2);
printf("Enter Description: \n");
scanf("%s", &descriptionI);
printf("Enter Quantity: \n");
scanf("%d", &qtyI);
printf("Enter Order Quantity: \n");
scanf("%s", &ordqtyI);

while (fscanf(fp4, "%s %s %d %s\n", &namet2, &description2, &qty2, &ordqty2) != EOF){
    if(namet2 != nameIt2)
        fprintf(fpt2, "%s %s %d %s\n", &namet2, &description2, qty2, &ordqty2);
}

`scanf("%s", &variable` looks fishy. The array name "decays" into a pointer to the first element, so the & is either unnecessary or a severe bug, depending on the variable types. — Lundin, Jan 09 '13 at 10:28

score 72 · Answer 1 · edited Jun 02 '17 at 20:02

72

To compare two C strings (char *), use strcmp(). The function returns 0 when the strings are equal, so you would need to use this in your code:

if (strcmp(namet2, nameIt2) != 0)

If you (wrongly) use

if (namet2 != nameIt2)

you are comparing the pointers (addresses) of both strings, which are unequal when you have two different pointers (which is always the case in your situation).

edited Jun 02 '17 at 20:02

Peter Mortensen

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answered Jan 09 '13 at 10:23

Veger

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score 15 · Answer 2 · edited Dec 04 '16 at 11:21

For comparing 2 strings, either use the built in function strcmp() using header file string.h

if(strcmp(a,b)==0)
    printf("Entered strings are equal");
else
    printf("Entered strings are not equal");

OR you can write your own function like this:

int string_compare(char str1[], char str2[])
{
    int ctr=0;

    while(str1[ctr]==str2[ctr])
    {
        if(str1[ctr]=='\0'||str2[ctr]=='\0')
            break;
        ctr++;
    }
    if(str1[ctr]=='\0' && str2[ctr]=='\0')
        return 0;
    else
        return -1;
}

simonc · Answer 3 · 2013-01-09T10:29:31.563

7

You are currently comparing the addresses of the two strings.

Use strcmp to compare the values of two char arrays

 if (strcmp(namet2, nameIt2) != 0)

edited Jan 09 '13 at 10:29

answered Jan 09 '13 at 10:23

simonc

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score 3 · Answer 4 · answered Jan 09 '13 at 10:24

3

You try and compare pointers here, not the contents of what is pointed to (ie, your characters).

You must use either memcmp or str{,n}cmp to compare the contents.

answered Jan 09 '13 at 10:24

fge

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score 2 · Answer 5 · answered Jan 09 '13 at 10:24

2

You need to use strcmp:

strcmp(namet2, nameIt2)

answered Jan 09 '13 at 10:24

jgr

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score 2 · Answer 6 · edited Dec 04 '16 at 11:27

2

The name of the array indicates the starting address. Starting address of both namet2 and nameIt2 are different. So the equal to (==) operator checks whether the addresses are the same or not. For comparing two strings, a better way is to use strcmp(), or we can compare character by character using a loop.

edited Dec 04 '16 at 11:27

Nisse Engström

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answered Jan 09 '13 at 11:27

Rajesh

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score 1 · Answer 7 · answered Dec 28 '16 at 17:23

To answer the WHY in your question:

Because the equality operator can only be applied to simple variable types, such as floats, ints, or chars, and not to more sophisticated types, such as structures or arrays. To determine if two strings are equal, you must explicitly compare the two character strings character by character.

score 0 · Answer 8 · answered Aug 02 '14 at 19:00

if(strcmp(sr1,str2)) // this returns 0 if strings r equal 
    flag=0;
else flag=1; // then last check the variable flag value and print the message 

                         OR

char str1[20],str2[20];
printf("enter first str > ");
gets(str1);
printf("enter second str > ");
gets(str2);

for(int i=0;str1[i]!='\0';i++)
{
    if(str[i]==str2[i])
         flag=0;
    else {flag=1; break;}
}

 //check the value of flag if it is 0 then strings r equal simple :)

Comparing two strings in C?

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