C - Converting array of char into lower case

Question

Currently I have websites store in char *banned[100] and I want to convert them all into lowercase using:

char *banned[100];
int x = 0;
if(fgets(temp, 100, file) != NULL) {
        char *tempstore;
        tempstore = (char*) malloc(sizeof(temp));
        strcpy(tempstore, temp);
        banned[x] = tempstore;
        x++;
    }
char temps[100];        
while(banned[c]){
        temps[c]=putchar(tolower(*banned[c]));
        c++;
}

But the results are not what I'm expecting. Can I get some tips/hints on what I'm doing wrong?

What is putchar() doing there? What do you think it does? Also note that banned is an array of 100 char* (string) elements, while temps is an array of 100 char (character) elements. temps is a string by itself; it is not an array of strings. — cdhowie
– cdhowie, Commented Nov 21, 2014 at 4:55
Ohh I wasnt aware of that.. Thanks for the telling me! I'm still very new to C :P — Piglet
– Piglet, Commented Nov 21, 2014 at 5:04

Ryan · Accepted Answer · 2014-11-21 05:17:46Z

4

Since you know the size of the string (char array), you can just use a for loop.

char temps[100];
size_t i;

for(i = 0; i < 100; i++)
  temps[i] = tolower(temps[i]);

edited Nov 21, 2014 at 5:17

answered Nov 21, 2014 at 4:58

Ryan

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5 Comments

cdhowie Over a year ago

The if conditional is redundant; tolower() will perform this same test.

Piglet Over a year ago

My values are stored in char *banned[100] so that wouldn't work in my case.

cdhowie Over a year ago

@self Yes. Redundant code is bad. It provides zero benefit while giving bugs a place to hide.

ThunderPhoenix Over a year ago

It's bad idea to convert all chars in temps. You have stop at the last '\0' char.

shevy Over a year ago

Guys, it would be better if you actually update the answer with good suggestions. Most people will never read the comments here.

score 1 · Accepted Answer · 2014-11-21 06:14:48Z

1

Use the below code to meet your requirement,

char *strtolower(char *s)
{
    char *d = (char *)malloc(strlen(s));
    while (*s)
    {
        *d =tolower(*s);
        d++;
        s++;
    }
    return d;
}

int main(void)
{
    char *banned[100];
    char *temps[100];
    char temp[100];

    FILE *file = fopen("test.txt", "r");
    int x = 0;

    if (file != NULL)
    {
        while(fgets(temp, 100, file) != NULL)
        {
            char *tempstore;
            tempstore = (char *) malloc(sizeof(temp));
            strcpy(tempstore, temp);
            banned[x] = tempstore;
            x++;

            puts(tempstore);

        }

        int c = 0;

        while(c < x)
        {
            temps[c] = strtolower(banned[c]);
            puts(temps[c]);
            c++;
        }
    }
    return 0;
}

edited Nov 21, 2014 at 6:14

answered Nov 21, 2014 at 4:59

user4226071

14 Comments

Piglet Over a year ago

That would break another piece of my code where I store values into banned:

user4226071 Over a year ago

what break ? also you need to confirm the string banned is null terminated. That means, the end of string must be marked with '\0'.

Piglet Over a year ago

Oh sorry, I meant if I changed char *banned[100] to char banned[100], another part of the code will break. I've updated the question with more code. Sorry about the confusion!

user4226071 Over a year ago

you trying to read single entry in file ? or can be many entries ?

Piglet Over a year ago

The file can contain up to 100 website urls, which would each be on a different line

|

ThunderPhoenix · Accepted Answer · 2020-04-22 12:24:34Z

1

You can try this :

char temps[100];
size_t i;

for(i = 0; temps[i] != '\0'; i++)
  temps[i] = tolower(temps[i]);

answered Apr 22, 2020 at 12:24

ThunderPhoenix

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