1 | /* |
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2 | FUNCTION |
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3 | <<strncat>>---concatenate strings |
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4 | |
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5 | INDEX |
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6 | strncat |
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7 | |
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8 | SYNOPSIS |
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9 | #include <string.h> |
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10 | char *strncat(char *restrict <[dst]>, const char *restrict <[src]>, |
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11 | size_t <[length]>); |
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12 | |
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13 | DESCRIPTION |
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14 | <<strncat>> appends not more than <[length]> characters from |
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15 | the string pointed to by <[src]> (including the terminating |
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16 | null character) to the end of the string pointed to by |
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17 | <[dst]>. The initial character of <[src]> overwrites the null |
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18 | character at the end of <[dst]>. A terminating null character |
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19 | is always appended to the result |
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20 | |
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21 | WARNINGS |
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22 | Note that a null is always appended, so that if the copy is |
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23 | limited by the <[length]> argument, the number of characters |
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24 | appended to <[dst]> is <<n + 1>>. |
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25 | |
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26 | RETURNS |
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27 | This function returns the initial value of <[dst]> |
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28 | |
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29 | PORTABILITY |
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30 | <<strncat>> is ANSI C. |
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31 | |
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32 | <<strncat>> requires no supporting OS subroutines. |
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33 | |
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34 | QUICKREF |
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35 | strncat ansi pure |
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36 | */ |
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37 | |
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38 | #include <string.h> |
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39 | #include <limits.h> |
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40 | |
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41 | /* Nonzero if X is aligned on a "long" boundary. */ |
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42 | #define ALIGNED(X) \ |
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43 | (((long)X & (sizeof (long) - 1)) == 0) |
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44 | |
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45 | #if LONG_MAX == 2147483647L |
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46 | #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080) |
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47 | #else |
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48 | #if LONG_MAX == 9223372036854775807L |
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49 | /* Nonzero if X (a long int) contains a NULL byte. */ |
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50 | #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080) |
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51 | #else |
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52 | #error long int is not a 32bit or 64bit type. |
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53 | #endif |
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54 | #endif |
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55 | |
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56 | #ifndef DETECTNULL |
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57 | #error long int is not a 32bit or 64bit byte |
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58 | #endif |
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59 | |
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60 | char * |
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61 | strncat (char *__restrict s1, |
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62 | const char *__restrict s2, |
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63 | size_t n) |
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64 | { |
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65 | #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__) |
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66 | char *s = s1; |
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67 | |
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68 | while (*s1) |
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69 | s1++; |
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70 | while (n-- != 0 && (*s1++ = *s2++)) |
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71 | { |
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72 | if (n == 0) |
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73 | *s1 = '\0'; |
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74 | } |
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75 | |
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76 | return s; |
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77 | #else |
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78 | char *s = s1; |
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79 | |
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80 | /* Skip over the data in s1 as quickly as possible. */ |
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81 | if (ALIGNED (s1)) |
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82 | { |
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83 | unsigned long *aligned_s1 = (unsigned long *)s1; |
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84 | while (!DETECTNULL (*aligned_s1)) |
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85 | aligned_s1++; |
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86 | |
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87 | s1 = (char *)aligned_s1; |
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88 | } |
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89 | |
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90 | while (*s1) |
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91 | s1++; |
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92 | |
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93 | /* s1 now points to the its trailing null character, now copy |
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94 | up to N bytes from S2 into S1 stopping if a NULL is encountered |
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95 | in S2. |
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96 | |
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97 | It is not safe to use strncpy here since it copies EXACTLY N |
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98 | characters, NULL padding if necessary. */ |
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99 | while (n-- != 0 && (*s1++ = *s2++)) |
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100 | { |
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101 | if (n == 0) |
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102 | *s1 = '\0'; |
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103 | } |
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104 | |
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105 | return s; |
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106 | #endif /* not PREFER_SIZE_OVER_SPEED */ |
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107 | } |
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