C ++比较char数组与字符串 [英] C++ Compare char array with string

问题描述

我试图比较一个字符数组与一个字符串，如下：

  const char * var1 = 
 var1 = getenv（myEnvVar）; 
 
 if（var1 ==dev）
 {
 // do stuff 
} 
  $ p> 
 
 
这个if语句从不验证为true ...当我输出var1它是dev，我想或许它有一些与终止的字符串有关，但是dev和var1的strlen是相等的...我也认为可能var1 ==dev比较dev与var1的内存位置，而不是值。 * var1 ==dev会导致错误....尝试了很多东西，可能是一个简单的解决方案为saavy c ++开发人员（我havent编码c ++在一个悠闲的时间）。
 
 
 
编辑：
我们尝试了
  if（strcmp（var1，dev）== 0）
  
和
  if（strncmp（var1，dev，3）== 0）
  
谢谢
 
 
 
编辑：在家里测试后，我只是建议我的同事更改数据类型为字符串。我相信他正在比较一个大型字符数组对一个字符串。我把一个程序，输出sizeof，strlen等，以帮助我们通过它。感谢大家的帮助。
解决方案
使用  strcmp（） 来比较字符串的内容：
  if（strcmp（var1，dev）== 0）{
} 
  
说明：在C中，字符串是指向包含字节的内存位置的指针。使用等于运算符将 char * 比较到 char * 将无法正常工作，因为您正在比较字符串的内存位置，而不是它们的字节内容。例如 strcmp（）的函数将遍历这两个字符串，检查它们的字节，看它们是否相等。 如果strcmp（）相等，则返回0;如果它们不同，则返回非零值。有关详情，请参见手册页。
 
I'm trying to compare a character array against a string like so:
const char *var1 = " ";
var1 = getenv("myEnvVar");

if(var1 == "dev")
{
   // do stuff
}
This if statement never validates as true... when I output var1 it is "dev", I was thinking maybe it has something to do with a null terminated string, but the strlen of "dev" and var1 are equal... I also thought maybe var1 == "dev" was comparing "dev" against the memory location of var1 instead of the value. *var1 == "dev" results in an error.... tried many things, probably a simple solution for the saavy c++ developer (I havent coded c++ in a looong time).

edit:
we've tried
if(strcmp(var1, "dev") == 0)
and 
if(strncmp(var1, "dev", 3) == 0)
Thanks

edit: After testing at home I'm just going to suggest my co-worker changes the datatype to a string. I believe he was comparing a char array of a large size against a string. I put together a program that outputs sizeof, strlen, etc to help us work through it. Thanks to everyone for the help.
解决方案
Use strcmp() to compare the contents of strings:
if (strcmp(var1, "dev") == 0) {
}
Explanation: in C, a string is a pointer to a memory location which contains bytes. Comparing a char* to a char* using the equality operator won't work as expected, because you are comparing the memory locations of the strings rather than their byte contents. A function such as strcmp() will iterate through both strings, checking their bytes to see if they are equal. strcmp() will return 0 if they are equal, and a non-zero value if they differ. For more details, see the manpage.

                        
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