strlen | 易学教程

Is there a difference between $str == '' and strlen($str) == 0 in PHP?

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问题 As the title says: Is there a difference between $str == '' and strlen($str) == 0 in PHP? Is there any real speed difference and is one better to use than the other? 回答1: Yes, there is an important difference. The == operator does type conversion, so it's not always going to do what you expect. For example, (0 == "") returns true. So you're making an assumption that $str is actually a string. If you're sure this is the case, or if you don't care about the conversions, then it's fine.

Why reimplement strlen as loop+subtraction?

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问题 Inspired by this question about the following code from SQLite3: static int strlen30(const char *z){ const char *z2 = z; while( *z2 ){ z2++; } return 0x3fffffff & (int)(z2 - z); } that is accompanied by a commit message saying this function helps with int overflows. I'm particularly interested in this part: const char *z2 = z; while( *z2 ){ z2++; } to me this loop advances z2 until z2 points onto null terminator. Then z2-z yields the string length. Why not use strlen() for this part and

Length of string with \0 in it in C

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问题 Well I read input from user as: scanf("%[^\n]", message); And I initialise char message [100] =""; now, in another function I need to find out length of input in message, I did it easily with strlen() , unfortunately it doesn't work correctly when I do later in terminal echo -e "he\0llo" | .asciiart 50 It will read the whole input BUT strlen will only return length 2. Is there any other way I could find out length of input ? 回答1: By definition strlen stops on the null character you have to

strlen to return size_t?

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问题 In C: My string length function is returning a size_t value? Why is it not returning a integer which is conventional? And one more thing I noticed was that when I was trying concatenate this string with another string I received a bus error when I ran the program. Context: I was kind of playing with gmp library and converting big numbers to strings and I end up with the above situation. What kind of a string is that? Is my operating system playing a role in this issue? I use a MAC, 64-bit OS.

strlen() not working with string variable

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问题 #include <iostream> #include <string> #include <cstring> using namespace std; int main() { string b="hello"; cout<<b; int c = strlen(b); cout << "Hello world!" <<c<< endl; return 0; } When I try to run this I get the error below ||=== Build: Debug in strlen (compiler: GNU GCC Compiler) ===| C:\Users\Waters\Desktop\hellow world\strlen\main.cpp||In function 'int main()':| C:\Users\Waters\Desktop\hellow world\strlen\main.cpp|14|error: cannot convert 'std::string {aka std::basic_string<char>}' to

Use strlen with scanf(%ms)

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问题 Is it possible to use strlen() over a dynamically allocated string? FOR EXAMPLE : #include <stdio.h> #include <string.h> int main () { char *input=NULL; printf ("Enter a sentence: "); scanf("%ms", &input); //Is this legit? printf ("The sentence entered is %u characters long.\n",(unsigned)strlen(input)); return 0; } 回答1: You can use strlen() on any sequence of char s ended by a '\0' , the null-character aka NUL *1 , which in fact equals 0 . It does not matter how the memory has been allocated.

C: Custom strlen() library function

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问题 I created my version of strlen() function. unsigned int my_strlen(char *p) { unsigned int i = 0; while(*p!='\0') { i++; p++; } return i; } It gives me correct output everytime i run.But my collegues are saying this code may cause problem on systems where length of character is greater than 1 byte . Is that so ?? So they modified the code as following: unsigned int my_strlen(char *p) { unsigned int i = 0; char *start = p; while(*p!='\0') { i++; p++; } return p - start; } I always thought in C

Valgrind errors on simple C string functions

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问题 Let's consider this simple test program: #include <stdio.h> #include <string.h> int main(int argc, char *argv[]) { char buf[256]; int i; strcpy(buf,"Hello world!"); i = strlen(buf); printf("Length of string is %d.\n",i); return 0; } When compiling it with the Intel c++ compiler and optimizations turned on (O3), I get the following errors from valgrind: ==8727== Conditional jump or move depends on uninitialised value(s) ==8727== at 0x4009EF: main (strtest.cpp:11) ==8727== Use of uninitialised

C语言课设-单位车辆调度管理

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单位车辆信息包括：车牌号、车型、载重（客）量，车牌，生产厂家，出厂日期，购买日期，购买单价等；车辆调度信息还应包括：用车人，用车单位，调度人，出车车牌，出车司机，出车用途，出车日期，出车时间，收车日期，收车时间及出车费用等信息等。设计“车辆调度管理系统”，使之能提供以下功能：系统以菜单方式工作；车辆调度信息录入功能(车辆调度信息用文件vehicle.txt保存)；车辆信息及车辆调度信息浏览功能；车辆调度查询和排序功能：车辆信息及车辆调度信息的删除与修改等功能。代码如下，完全原创，代码功能完整！！ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <windows.h> int feature;//定义输入的功能选项 char now_date[12];//定义系统当前日期存储缓冲区 SYSTEMTIME sys; //定义系统时间变量 //定义车辆数据结构 typedef struct Vehicle { char *ver_id;//定义车辆编号 char *ver_no;//定义车辆牌号 char *weight;//定义车辆对应载重量 char *ver_trand;//定义车牌 char *factory;//定义车辆生产厂家 char *outdate;//定义车辆出厂日期

Is There A Difference Between strlen()==0 and empty()?

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问题 I was looking at some form validation code someone else had written and I saw this: strlen() == 0 When testing to see if a form variable is empty I use the empty() function. Is one way better than the other? Are they functionally equivalent? 回答1: strlen is to get the number of characters in a string while empty is used to test if a variable is empty Meaning of empty: empty("") //is empty for string empty(0) // is empty for numeric types empty(null) //is empty empty(false) //is empty for