如何將一個NSString數組轉換爲一個c數組的字符串？

Question

我有一個NSArray<NSString*>*對象，我需要調用一個C API，它接受一個字符串數組作爲char**。

這樣做的最好方法是什麼？重要說明是C字符串不能有const修改，所以像下面是不是因爲UTF8String回報const char*不夠好：

NSArray<NSString*>* names = ...; 
int len = args.count; 
char* cNames[len]; 
for(int i = 0; i < len; i++) { 
    cNames[i] = names[i].UTF8String; 
}; 

Answer 1

你會希望做一些動態內存，你可以不依賴UTF8String的後備內存正在發佈。

NSArray *strings = @[ @"String 1", @"Other string", @"Random String"]; 
char **cStrings = NULL; 
NSInteger numCStrings = strings.count; 

if (numCStrings) { 
    cStrings = (char **)calloc(numCStrings, sizeof(char*)) ; 

    if (cStrings) { 
     // Safer to allocate memory for each string 

     for (NSInteger i=0;i<numCStrings;i++) { 
      NSString *nsString = strings[i]; 
      char *cString = (char *)malloc([nsString lengthOfBytesUsingEncoding:NSUTF8StringEncoding] + 1); // + 1 for \0 

      if (cString) { 
       strcpy(cString, nsString.UTF8String); 
       cStrings[i] = cString; 
      } else { 
       // You should handle your error 
      } 
     } 
    } else { 
     // You should handle your error 
    } 
} 

for (NSInteger i=0;i<numCStrings;i++) { 
    NSLog(@"C-String (%ld): %s", i, cStrings[i]); 
} 

// Note you need to free your memory later! 
// Do any additional setup after loading the view, typically from a nib. 
for (NSInteger i=0;i<numCStrings;i++) { 
    if (cStrings[i]) { 
     // Free each string 
     free(cStrings[i]); 
    } 
} 

// Free the array 
free(cStrings); 

cStrings = NULL; 
numCStrings = 0;