架构x86_64的未定义符号:"_gets_s"

Question

我试图从Beginning C 5th Ed这本书编译一个示例程序.作者:Ivor Horton.试图在OSX上编译它,我从gcc获得以下输出:

$ gcc program6_07.c 
program6_07.c:18:59: warning: format specifies type 'int' but the argument has
      type 'size_t' (aka 'unsigned long') [-Wformat]
          "Terminate input by entering an empty line:\n", str_len);
                                                          ^~~~~~~
program6_07.c:23:5: warning: implicit declaration of function 'gets_s' is
      invalid in C99 [-Wimplicit-function-declaration]
    gets_s(buf, buf_len);                                  // Read a lin...
    ^
program6_07.c:24:9: warning: implicit declaration of function 'strnlen_s' is
      invalid in C99 [-Wimplicit-function-declaration]
    if(!strnlen_s(buf, buf_len))                           // Empty lin...
        ^
program6_07.c:27:8: warning: implicit declaration of function 'strcat_s' is
      invalid in C99 [-Wimplicit-function-declaration]
    if(strcat_s(str, str_len, buf))                        // Concatenat...
       ^
program6_07.c:33:60: warning: data argument not used by format string
      [-Wformat-extra-args]
  printf("The words in the prose that you entered are:\n", str);
         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  ^
program6_07.c:37:18: warning: implicit declaration of function 'strtok_s' is
      invalid in C99 [-Wimplicit-function-declaration]
  char * pWord = strtok_s(str, &str_len, delimiters, &ptr);  // Find 1st word
                 ^
program6_07.c:37:10: warning: incompatible integer to pointer conversion
      initializing 'char *' with an expression of type 'int' [-Wint-conversion]
  char * pWord = strtok_s(str, &str_len, delimiters, &ptr);  // Find 1st word
         ^       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
program6_07.c:45:13: warning: incompatible integer to pointer conversion
      assigning to 'char *' from 'int' [-Wint-conversion]
      pWord = strtok_s(NULL, &str_len, delimiters, &ptr);    // Find sub...
            ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
8 warnings generated.
Undefined symbols for architecture x86_64:
  "_gets_s", referenced from:
      _main in program6_07-4a1c4c.o
  "_strcat_s", referenced from:
      _main in program6_07-4a1c4c.o
  "_strnlen_s", referenced from:
      _main in program6_07-4a1c4c.o
  "_strtok_s", referenced from:
      _main in program6_07-4a1c4c.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

该计划的代码如下:

// Program 6.7 Find all the words
#define __STDC_WANT_LIB_EXT1__ 1                           // Make optional versions of functions available
#include <stdio.h>
#include <string.h>
#include <stdbool.h>

int main(void)
{
  char delimiters[] = " \".,;:!?)(";                       // Prose delimiters
  char buf[100];                                           // Buffer for a line of keyboard input
  char str[1000];                                          // Stores the prose to be tokenized
  char* ptr = NULL;                                        // Pointer used by strtok_s()
  str[0] = '\0';                                           // Set 1st character to null

  size_t str_len = sizeof(str);
  size_t buf_len = sizeof(buf);
  printf("Enter some prose that is less than %d characters.\n"
          "Terminate input by entering an empty line:\n", str_len);

  // Read multiple lines of prose from the keyboard
  while(true)
  {
    gets_s(buf, buf_len);                                  // Read a line of input
    if(!strnlen_s(buf, buf_len))                           // Empty line ends input
      break;

    if(strcat_s(str, str_len, buf))                        // Concatenate the line with str
    {
      printf("Maximum permitted input length exceeded.");
      return 1;
    }
  }
  printf("The words in the prose that you entered are:\n", str);

  // Find and list all the words in the prose
  unsigned int word_count = 0;
  char * pWord = strtok_s(str, &str_len, delimiters, &ptr);  // Find 1st word
  if(pWord)
  {
    do
    {
      printf("%-18s", pWord);
      if(++word_count % 5 == 0)
        printf("\n");
      pWord = strtok_s(NULL, &str_len, delimiters, &ptr);    // Find subsequent words
    }while(pWord);                                           // NULL ends tokenizing
    printf("\n%u words found.\n", word_count);
  }
  else
    printf("No words found.\n");

  return 0;
}

我以为我已经定义了可选功能,但我想我没有？这只是一本陈旧的书或一个坏的例子,还是我在尝试编译时做错了什么？

Answer 1

该gets_s()功能在ISO/IEC 9899:2011的附录K,当前的C标准和TR 24731-1中定义.这是可选的.它没有被广泛实现 - 事实上,它基本上只能在使用Microsoft C库的Microsoft系统上使用.类似的评论适用于其他_s功能 - 它们在附录K中定义,除了微软的编译器外,通常不会在任何地方实现.

请注意,您可以通过测试是否__STDC_LIB_EXT1__由编译器设置来测试附件K函数在一般情况下是否可用.它应具有200509L与原始TR 24731-1一致的值或201112L符合附件K.如果由实现定义,则您的代码应定义__STDC_WANT_LIB_EXT1__为暴露附件K功能的定义.

您将需要使用不同的功能:

• 因为gets_s(),标准fgets()可能是最接近的,但它包括输入末尾的换行符,而gets_s()不是.另外,gets_s()在错误上截断输出字符串 - 如果在没有剩余空格之前没有换行符; 如果发生这种情况,它也会读到下一个换行符.该fgets()功能不会执行任何操作.
• 用于strnlen_s(),使用strnlen(),可在macOS Sierra(和Mac OS X)和Linux上使用.
• 对于strcat_s(),可能使用strlcat(),再次在macOS Sierra和Linux上可用.
• 对于strtok_s(),可能使用strtok_r(),这是POSIX的标准部分.请注意,接口与接口strtok_r()不同strtok_s(),但功能基本相同.