CODEWITHSUNDEEP
c
Simone Greco
Simone Greco

Reputation: 13

How do I truncate string with an offset function in c?

I would like to truncate a string with a function.
I am getting the error: main.c:7: error: lvalue expected

What am I doing wrong?

char *stringtest;

int main() 
{
    &stringtest=strtrunk("hello world!", 3);
    printf("%s", &stringtest);

    return 0;
}

char *strtrunk(char *string, int offset)
{
    int stringlen = strlen(string);
    string[stringlen - offset] = 0;
    return string;
}

Upvotes: 0

Views: 251

Answers (3)

Spikatrix
Spikatrix

Reputation: 20244

Your function strtrunk returns a char* and stringtest is already of type char*. So use 

stringtest=strtrunk("hello world!", 3);

instead of

&stringtest=strtrunk("hello world!", 3);

%s expects a char* as its argument and since stringtest is already a char*, use

printf("%s", stringtest);

instead of

printf("%s", &stringtest);

The error "lvalue expected" occurs because &stringtest isn't a valid lvalue.

Oh, and as mentioned in other answers, modifying a string literal invokes Undefined Behavior.

And you need to add a function prototype just after including the headers:

char* strtrunk(char*, int);

or otherwise simply move the definition of strtrunk before the definition of main.

Upvotes: 3

Sorcrer
Sorcrer

Reputation: 1644

You can use the below code

char *strtrunk(char *string, int offset);
char *stringtest;
char Char_array[]="hello world!";
int main() 
{
    stringtest=strtrunk(Char_array, 3);
    printf("%s", stringtest);
    getch();
    return 0;
}

char *strtrunk(char *string, int offset)
{
    int stringlen = strlen(string);
    string[stringlen - offset] = 0x00;
    return string;
}

Please read this link which explains your problem in detail Why do I get a segmentation fault when writing to a string initialized with "char *s" but not "char s[]"?

Upvotes: 0

Sumit Trehan
Sumit Trehan

Reputation: 4035

Make the changes as suggested by CoolGuy. However that won't be sufficient.

You cannot modify a string literal. Even if your program would compile, it would crash since it is illegal to modify the string literal. Use something i have shown below:

char p[20] = "hello world!"
strtrunk (p, 3);

Upvotes: 0

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