strncpy不能正确存储字符C

Question

基本上，我使用strncpy截断字符，如果它大于字符数组大小。

所以，我有以下变量和方法。

char studentName[6]; 
char colour[5]; 
char music[7]; 

strcpy(this->studentName, "null"); 
strcpy(this->colour, "null"); 
strcpy(this->music, "null"): 

void setName (char* studentName) 
{ 
strncpy(this->studentName, studentName, 6); 
this->studentName[6] = '\0'; // SET LAST TO NULL POINTER 
} 

void setColour (char* colour) 
{ 
strncpy(this->colour, colour, 5); 
this->colour[5] = '\0'; // SET LAST TO NULL POINTER 
} 

void setMusic (char* music) 
{ 
strncpy(this->music, music, 7); 
this->music[7] = '\0'; // SET LAST TO NULL POINTER 
} 

所以，如果我设置了学生的名字Jackson，它将截断至Jackso，但是，我的colour变量将是空白，我music变量将是null。

另外，如果我尝试...

void setName (char* studentName) 
{ 
    strncpy(this->studentName, studentName, 6); 
    this->studentName[6-1] = '\0'; // SET LAST TO NULL POINTER 
} 

void setColour (char* colour) 
{ 
strncpy(this->colour, colour, 5); 
this->colour[5-1] = '\0'; // SET LAST TO NULL POINTER 
} 

void setMusic (char* music) 
{ 
strncpy(this->music, music, 7); 
this->music[7-1] = '\0'; // SET LAST TO NULL POINTER 
} 

，我设置了学生的名字Jackson我得到这样的Jacksonull。它将null添加到末尾

Answer 1

尝试使用sizeof()而不是原始数字。它允许你改变数组的大小，而不用接触你的代码。

您首先复制sizeof(array)-1符号，然后设置索引为sizeof(array)-1（因为索引从0开始）到'\0'的最后一个符号。

您的代码编辑应该是这样的：

char studentName[6]; 
char colour[5]; 
char music[7]; 

strcpy(this->studentName, "null"); 
strcpy(this->colour, "null"); 
strcpy(this->music, "null"): 

void setName (char* studentName) 
{ 
strncpy(this->studentName, studentName, sizeof(this->studentName)-1); // Copy n-1 chars 
this->studentName[sizeof(this->studentName)-1] = '\0'; // n is set to null symbol 
} 

void setColour (char* colour) 
{ 
strncpy(this->colour, colour, sizeof(this->color)-1); 
this->colour[sizeof(this->color)-1] = '\0'; 
} 

void setMusic (char* music) 
{ 
strncpy(this->music, music, sizeof(this->music)-1); 
this->music[sizeof(this->music)-1] = '\0'; 
} 

Answer 2

这里（假设Linux平台上你可能有，如果你在Windows，而不是一定要取是strlcpy执行。）

#include <bsd/string.h> 

char studentName[6]; /* Good to know: Globals are initialized to zero */ 
char colour[5]; 
char music[7]; 

/* Pretty useless function since a single strlcpy call is enough */ 
static size_t setX(char *buf, size_t buflen, const char *new_val) { 
    return strlcpy(buf, new_val, buflen); 
} 

int main(int argc, char **argv) { 
    setX(studentName, 6, "Peter"); /* Please read man page and check return value */ 
} 

现在strlcpy只要长度参数> 0，就保证NUL终止。