CODEWITHSUNDEEP
cstringstrlen
user8304242
user8304242

Reputation:

Avoid adding another '\0' if string already has one?

it is not clear if + 1 is needed or not here:

int len = strlen(TARGET);
info = malloc( len + 1 );

because few lines above it it already was once appended to it:

TARGET[END - START] = '\0';

if it is needed then perhaps also.. appending the \0 is needed.

int len = strlen(TARGET);
info = malloc( len + 1 );
strcpy(info, TARGET);
info[len] = '\0';

Q: How to determine if a string already has the null termination

perhaps if it already has it.. appending another one wouldn't be logic.

full function :

char * FUNCTION ( char * v ){

char *TARGET = NULL;
const char *PATTERN1 = "co=";
const char *PATTERN2 = "&";
char *START = strstr(v, PATTERN1);

if (START) {
START = START + strlen(PATTERN1);
char *END = strstr(START, PATTERN2);
if (!END){
END = START + strlen(START);
}
TARGET = malloc(END - START + 1);
memcpy(TARGET, START, END - START);
TARGET[END - START] = '\0';
}

if (!START || TARGET == NULL || TARGET[0] == '\0') {
return 0;
}

int len = strlen(TARGET);
info = malloc( len + 1 );
strcpy(info, TARGET);
info[len] = '\0';

return info;
}

Upvotes: 1

Views: 75

Answers (3)

Federico klez Culloca
Federico klez Culloca

Reputation: 27139

strlen calculates how many characters there are in a string up to and excluding the \0, so you'll never count it. So for example if you string is "hello", its strlen would be 5. So yes, you'll always need to add 1 to its length to account for the \0 at the end.

Upvotes: 3

Sourav Ghosh
Sourav Ghosh

Reputation: 134386

How to determine if a string already has the null termination

Well, a "string", is by definition, null-terminated. Otherwise, it is not a string.

Quoting C11, chapter §7.1.1

A string is a contiguous sequence of characters terminated by and including the first null character. [....]

From theoretical point of view, it's the responsibility of the producer, not the consumer, to ensure the null-termination for a character array which is supposed to be used as string.

That said, strlen() returns the length of a string, without the null-terminator. So, if you were to use the return value of strlen() of an existing string to allocate memory for a copy thereof, you need to allocate one extra bye for the null-terminator, so the +1 is required while passing the size to allocator function.

Upvotes: 5

Mike Nakis
Mike Nakis

Reputation: 62120

The following:

int len = strlen(TARGET);

will not give you sizeof(TARGET); it will just count the number of characters before the first \0. So, if TARGET contains "a\0bcd" it will give you just 1 (for 'a').

The following:

 info = malloc( len +1 );

Needs to allocate enough bytes for the string plus the null terminator, so the + 1 is necessary.

The following:

strcpy(info, TARGET);

will copy characters until the first '\0' is encountered, and then it will append a '\0', so there must be enough space in the destination for the '\0'.

Upvotes: 1

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