2D陣列和雙指針用C

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2D arrays and pointers.
(This is not a duplicate of that question. In that question the OP was correctly passing a pointer-to-a-pointer, and the problem was with dereferencing an uninitialised pointer. This question is about passing trying to pass a pointer-to-array to a function that expects a pointer-to-a-pointer.)2D陣列和雙指針用C

對於一些現有的代碼兼容的，我需要一個二維數組傳遞給一個函數作爲指針到一個指針。我簡化了下面的代碼。在功能printvalues中打印出結構中的第一個值並newptr，即「我的值是123並在結構123中」後，我得到一個seg。故障。我錯過了什麼？

#include <stdio.h> 
#include <stdlib.h> 

typedef struct mystruct 
{ 
    char mychar [4][5]; 
} mystruct_t; 

void printvalues(char** newptr) 
{ 
    int i; 
    mystruct_t * fd = (mystruct_t*)malloc(sizeof(*fd)); 
    for (i = 0; i < 3; i++) 
    { 
    strcpy(fd->mychar[i], newptr[i]); 
    printf("My value is %s and in struct %s\n", newptr[i], fd->mychar[i]); 
    } 
} 

int main(int argc, char **argv) 
{ 
    int i; 
    char *ptr = malloc(4*sizeof(char)); 
    char **pptr = (char **) malloc(5*sizeof(char *)); 

    char abc[4][5] = { "123", "456", "789" }; 

    for (i = 0; i < 3; i++) 
    { 
     printf("My value is %s\n", abc[i]); 
    } 

    ptr = abc; 
    printvalues(&ptr); 
}

來源

2011-06-06 lostinpointers

@lostinpointers：請不要簡單地轉發同樣的問題。如果你認爲這是一個不同的問題，你應該（1）承認先前的問題，（2）說明你從那時起做了什麼，（3）具體說明這個問題是如何新的。 – dmckee 2011-06-06 18:52:00

行：'ptr = abc;'（從下到上第三個）給我一個錯誤： '警告：從不兼容的指針類型賦值。 – 2011-06-06 18:52:06

值得指出的是，雖然你可以用'foo [] []'來訪問存儲在'char **'中的數據，但它與* char [] []'不是同一件事物。 – dmckee 2011-06-06 18:53:52

如果你有一個二維數組（像你這樣做ABC），你只提領的尺寸之一，你不能誠實指望它解析爲一個字符。它將解析爲該行字符的地址。

char abc[4][5] = { "123", "456", "789" }; 

for (i = 0; i < 3; i++) 
{ 
    printf("My value is %s\n", abc[i]); 
}

是沒有意義的。你需要更多的東西：

char abc[4][5] = { "123", "456", "789" }; 

for (i = 0; i < 3; i++) 
{ 
    for (j = 0; j < 4; j++) 
    { 
    printf("My value is %c\n", abc[i][j]); 
    } 
}

來源

2011-06-06 18:53:14

2D陣列和雙指針用C

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