How to convert string (char *) to upper or lower case in C

Question

How to convert string (char *) to upper or lower case in C

I have a structure:

typedef struct entry {
char *surname;
int house_no;
char *postcode;
} BEntry;

and a function to convert strings to uppercase:

void toUpper(char *str){
    while (*str != '\0')
    {
        *str = toupper(*str);
        str++;
    }
}

and in my main function I am assigning values to structure members and want to convert the last name to upper case:

mentry->surname = "bob";
mentry->house_no = 17;
mentry->postcode = "GK116BY";
toUpper(me->surname);

What is the correct way to convert a string to uppercase by passing a char pointer to a function like this? My program is returning a segmentation fault. Any help is greatly appreciated, thanks.

+3

c pointers char tolower toupper

Highway62 06 nov. 14 at 18:39

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3 answers

String literals such as "Hello, World!"

cannot be written. Or duplicate the string literal:

hw = strdup("Hello, World!");

or declare a variable char[]

and initialize it to a string literal. As a special case, string literals used in this way can be written:

char hw[] = "Hello, World!";

+1

fuz 06 nov. 14 at 18:43

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The easiest way to convert char *

to lower or upper case in c is withstrdup

#include <string.h>

char    *to_uppercase(char *s)
{
    int i = 0;
    char    *str = strdup(s);

    while (str[i])
    {
        if (str[i] >= 97 && str[i] <= 122)
            str[i] -= 32;
        i++;
    }
    return (str);
}

+1

julekgwa June 17. 16 at 21:34

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FatalError · Accepted Answer · 2014-11-06T18:42:40+0000

Your implementation toUpper()

should work fine. However, you should pay attention to your compiler warnings (or turn on warning levels if you didn't get them), you should see something when you assign a string literal to char *

like this). String literals const

, i.e. They cannot be changed. When you try to write to them, it will cause the segmentation fault you see.

You need something like:

mentry->surname = malloc(4);
strcpy(mentry->surname, "bob");

or more convenient, but not part of the standard C path:

mentry->surname = strdup("bob");

And of course, be sure to call free()

later anyway.

How to convert string (char *) to upper or lower case in C

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