A standard C function that returns the length of a string.
This function calculates the length of the string, excluding the terminating null byte \0. It is defined in the <string.h> standard header.
Questions tagged [strlen]
692 questions
304
votes
9 answers
Why does glibc's strlen need to be so complicated to run quickly?
I was looking through the strlen code here and I was wondering if the optimizations used in the code are really needed? For example, why wouldn't something like the following work equally good or better?
unsigned long strlen(char s[]) {
unsigned…
user11954200
171
votes
12 answers
Add ... if string is too long PHP
I have a description field in my MySQL database, and I access the database on two different pages, one page I display the whole field, but on the other, I just want to display the first 50 characters. If the string in the description field is less…
mais-oui
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113
votes
18 answers
Will strlen be calculated multiple times if used in a loop condition?
I'm not sure if the following code can cause redundant calculations, or is it compiler-specific?
for (int i = 0; i < strlen(ss); ++i)
{
// blabla
}
Will strlen() be calculated every time when i increases?
daisy
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90
votes
10 answers
Finding the length of a Character Array in C
What is a way in C that someone could find the length of a character array?
I will happily accept pseudo-code, but am not averse to someone writing it out if they'd like to :)
not_l33t
- 1,315
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45
votes
3 answers
Sizeof vs Strlen
#include
#include
int main(int argc, char *argv[]) {
char string[] = "october"; // 7 letters
strcpy(string, "september"); // 9 letters
printf("the size of %s is %d and the length is %d\n\n", string,
…
beparas
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38
votes
6 answers
strlen not checking for NULL
Why is strlen() not checking for NULL?
if I do strlen(NULL), the program segmentation faults.
Trying to understand the rationale behind it (if any).
hari
- 9,439
- 27
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36
votes
5 answers
Unexpected optimization of strlen when aliasing 2-d array
Here is my code:
#include
#include
typedef char BUF[8];
typedef struct
{
BUF b[23];
} S;
S s;
int main()
{
int n;
memcpy(&s, "1234567812345678", 17);
n = strlen((char *)&s.b) / sizeof(BUF);
…
M.M
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36
votes
4 answers
strlen in the C preprocessor?
Is it possible to implement strlen() in the C preprocessor?
Given:
#define MYSTRING "bob"
Is there some preprocessor macro, X, which would let me say:
#define MYSTRING_LEN X(MYSTRING)
Joby Taffey
- 1,129
- 1
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29
votes
5 answers
Determine #defined string length at compile time
I have a C-program (an Apache module, i.e. the program runs often), which is going to write() a 0-terminated string over a socket, so I need to know its length.
The string is #defined as:
#define POLICY "\n" \
"
Alexander Farber
- 21,519
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28
votes
10 answers
Where is the implementation of strlen() in GCC?
Can anyone point me to the definition of strlen() in GCC? I've been grepping release 4.4.2 for about a half hour now (while Googling like crazy) and I can't seem to find where strlen() is actually implemented.
Chris Tonkinson
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- 90
27
votes
1 answer
strlen - the length of the string is sometimes increased by 1
I'm doing some C puzzle questions. In most cases, I am able to find the right answer, but with that one I am having problems. I know the right answer by using the compiler, but I don't know the reason.
Have a look at the code:
char c[] =…
Prz3m3k
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25
votes
8 answers
Is using strlen() in the loop condition slower than just checking for the null character?
I have read that use of strlen is more expensive than such testing like this:
We have a string x 100 characters long.
I think that
for (int i = 0; i < strlen(x); i++)
is more expensive than this code:
for (int i = 0; x[i] != '\0'; i++)
Is it true?…
user466534
25
votes
3 answers
REPNZ SCAS Assembly Instruction Specifics
I am trying to reverse engineer a binary and the following instruction is confusing me, can anyone clarify what exactly this does?
=>0x804854e: repnz scas al,BYTE PTR es:[edi]
0x8048550: not ecx
Where:
EAX: 0x0
ECX: 0xffffffff
EDI:…
Michael Scott
- 539
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23
votes
4 answers
strlen() php function giving the wrong length of unicode characters
I am trying to get the length of this unicode characters string
$text = 'نام سلطان م';
$length = strlen($text);
echo $length;
output
20
How it determines the length of unicode characters string?
Munib
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23
votes
3 answers
format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘size_t’ [-Wformat]
I have searched about this warning and everyone had some mistake in their code, but here is something very unexpected I could not figure out . We do expect strlen(x) to be an integer but what does this warning tell me? How couldn't strlen be int?
In…
Optimus Prime
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