这个C代码有什么问题？ [英] Whats wrong with this C code?

问题描述

我的源代码：

  #include< stdio.h> 
 
 int main（）
 {
 char myArray [150]; 
 int n = sizeof（myArray）; 
 for（int i = 0; i< n; i ++）
 {
 myArray [i] = i + 1; 
 printf（％d\\\
，myArray [i]）; 
} 
返回0; 
 
 
 
 $ b我使用Ubuntu 14和gcc编译它，是： 
 
 
  1 
 2 
 3 
 ... 
 125 
 126 
 127 
 -128 
 -127 
 -126 
 -125 
 ... 
  
 
 
 
为什么它不会只计算到150？
解决方案
看来你的编译器默认认为类型 char 类型 signed char 。在这种情况下， CHAR_MIN 等于 SCHAR_MIN ，然后等于 -128 ，同时 CHAR_MAX 等于 SCHAR_MAX ，并且依次等于 127 （见标题< limits.h> ）
 
 
根据C标准（6.2 .5类型）
 
 
 
 
 15三种类型的char，signed char和unsigned char是
，统称为字符类型。实现将
定义char与
具有相同的范围，表示形式和行为，包括带符号字符或无符号字符 
 
 
对于签名类型，一位用作符号位。因此，对于类型 signed char ，最大值对应于以十六进制表示的表示形式
  0x7F 
  
等于127.最重要的位是有符号位，等于0.  
 
 
对于负值，有符号位设置为1，例如 -128 表示为
  0x80 
  
在程序中，存储在char中的值达到了正值最大值 0x7F ，并增加到等于 0x80 在十进制表示法中等于 -128 。
 
 
 
您应该明确地使用类型<$ c $如果您希望程序执行的结果不依赖于编译器设置，请使用c> unsigned char 而不是 char 。
 
 
 
或者在printf语句中，您可以显式类型 char 键入 unsigned char 。例如
  printf（％d \ n，（unsigned char）myArray [i]）; 
  
或者比较您可以在循环中写入的结果 
 
 
  printf（％d％d \ n，myArray [i]，（unsigned char）myArray [i]）; 
  
 
My sourcecode:
#include <stdio.h>

int main()
{
    char myArray[150];
    int n = sizeof(myArray);
    for(int i = 0; i < n; i++)
    {
        myArray[i] = i + 1; 
        printf("%d\n", myArray[i]); 
    }
    return 0;
}
I'm using Ubuntu 14 and gcc to compile it, what it prints out is:
1
2
3
...
125
126
127
-128
-127
-126
-125
...
Why doesn't it just count up to 150?
解决方案
It seems that your compiler by default considers type char like type signed char. In this case CHAR_MIN is equal to SCHAR_MIN and in turn equal to -128 while CHAR_MAX is equal to SCHAR_MAX and in turn equal to 127 (See header <limits.h>)

According to the C Standard (6.2.5 Types)

  
15 The three types char, signed char, and unsigned char are
  collectively called the character types. The implementation shall
  define char to have the same range, representation, and behavior as
  either signed char or unsigned char
For signed types one bit is used as the sign bit. So for the type signed char the maximum value corresponds to the following representation in the hexadecimal notation
0x7F
and equal to 127. The most significant bit is the signed bit and is equal to 0.

For negative values the signed bit is set to 1 and for example -128 is represented like
0x80
When in your program the value stored in char reaches its positive maximum 0x7Fand was increased it becomes equal to 0x80 that in the decimal notation is equal to -128.

You should explicitly use type unsigned char instead of the char if you want that the result of the program execution did not depend on the compiler settings.

Or in the printf statement you could explicitly cast type char to type unsigned char. For example
printf("%d\n", ( unsigned char )myArray[i]); 
Or to compare results you could write in the loop
printf("%d %d\n", myArray[i], ( unsigned char )myArray[i]); 


                        
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