结构返回字符数组打印值的两倍

Question

这是一个简单的程序，其中函数abc返回一个数组。但输出是

Thanks 
abcdefThanks 

为什么这样？我想谢谢只能打印一次。 此外，我需要把a的大小定为6.在这个程序中，没关系，但我正在做原始套接字编程，我需要它。大小= 6在那里预定义的头文件中声明。我怎样才能实现它？

char *abc() 
{ 
    unsigned char *ch; 
    unsigned char a[7],c[6]; 
    strncpy(a,"Thanks",strlen("Thanks")); 
    strncpy(c,"abcdef",strlen("abcdef")); 
    ch=malloc(50); 
    memset(ch,0,50); 
    memcpy(ch,&a,strlen(a)); 
    memcpy(ch+strlen(a)+1,&c,strlen(c)); 
    return ch; 
} 
int main() 
{ 
    char *a; 
    a=abc(); 
    printf("\n%s\n",a); 
    printf("\n%s\n",(a+7)); 
    fflush(stdout); 
    return 0; 
} 

谢谢:)

Answer 1

调用strlen(a)不停止你认为它应该因为没有零终结符和垃圾内存破坏你的结果。 的strlen（字符串）不包括零终止的计数

你还是请执行下列操作（看评论）

char *abc() 
{ 
    char *ch; 
    char a[7],c[7]; 
    strncpy(a,"Thanks",strlen("Thanks")); // Watch out, strlen(string) doesn't include null terminator 
    a[6] = '\0'; // Prevent garbage from uninitialized memory to pester your ch and strlen(a) 
    strncpy(c,"abcdef",strlen("abcdef")); 
    c[6] = '\0'; 
    ch=malloc(50); 
    memset(ch,0,50); 
    memcpy(ch,&a,strlen(a)); 
    memcpy(ch+strlen(a),&c,strlen(c)); // No -1 because you want to cut the terminator off 
    return ch; 
} 
int main() 
{ 
    char *a; 
    a=abc(); 
    printf("\n%s\n",a); 
    printf("\n%s\n",(a+7)); 
    fflush(stdout); 
    return 0; 
} 

以上编译使用C++，但它应该很很少有相同的调整。

这里是有记忆就像倾销，其中＃是指垃圾

char *abc() 
{ 
    char *ch; 
    char a[7],c[7]; 
    strncpy(a,"Thanks",strlen("Thanks")); // Watch out, strlen(string) doesn't include null terminator 
    // a = "Thanks##################################.." 
    a[6] = '\0'; // Prevent garbage from uninitialized memory to pester your ch and strlen(a) 
    // a = "Thanks\0############################" 
    strncpy(c,"abcdef",strlen("abcdef")); 
    // c = "abcdef############################" 
    c[6] = '\0'; 
    // c = "abcdef\0############################" 
    ch=malloc(50); 
    // ch = "###############################" 
    memset(ch,0,50); 
    // ch = "000000000000000000000000000000" 
    memcpy(ch,&a,strlen(a)); 
    // ch = "Thanks000000000000000000000000" 
    memcpy(ch+strlen(a),&c,strlen(c)); // No -1 because you want to cut the terminator off 
    // ch = "Thanksabcdef00000000000000000" 
    return ch; 
} 

Answer 2

你忘了零通过附加一个0字节终止您的字符串。

unsigned char a[7], c[7]; // 7 = 6+1 since "Thanks" and "abcdef" have 6 bytes 
strncpy (a, "Thanks", 6); 
a[6] = (char)0; 
strncpy (c, "abcdef", 6); 
c[6] = (char)0; 

您的c字符串太短而且没有明确的0结束。所以你的strlen(c)是undefined behavior