count_chars() 函数返回字符串中所用字符的信息（例如，ASCII 字符在字符串中出现的次数，或者某个字符是否已经在字符串中使用过）。
语法
count_chars(string,mode)
string 必需。规定要检查的字符串。
mode 可选。规定返回模式。默认是 0。以下是不同的返回模式：
0 - 数组，ASCII 值为键名，出现的次数为键值
1 - 数组，ASCII 值为键名，出现的次数为键值，只列出出现次数大于 0 的值
2 - 数组，ASCII 值为键名，出现的次数为键值，只列出出现次数等于 0 的值
3 - 字符串，带有所有使用过的不同的字符

4 - 字符串，带有所有未使用过的不同的字符

示例一

统计某个 ASCII 字符在字符串中出现次数

<?php
$str = "PHP is pretty fun!!";
$strArray = count_chars($str, 1);
foreach ($strArray as $key => $value) {
    echo "字符 <b>'" . chr($key) . "'</b> 被找到 $value 次。<br>";
} 
// 字符 ' ' 被找到 3 次。
// 字符 '!' 被找到 2 次。
// 字符 'H' 被找到 1 次。
// 字符 'P' 被找到 2 次。
// 字符 'e' 被找到 1 次。
// 字符 'f' 被找到 1 次。
// 字符 'i' 被找到 1 次。
// 字符 'n' 被找到 1 次。
// 字符 'p' 被找到 1 次。
// 字符 'r' 被找到 1 次。
// 字符 's' 被找到 1 次。
// 字符 't' 被找到 2 次。
// 字符 'u' 被找到 1 次。
// 字符 'y' 被找到 1 次。
?>

示例二

<?php
$str = "Hello World!";
print_r(count_chars($str,0)); // 模式0
// Array ( [0] => 0 [1] => 0 [2] => 0 [3] => 0 [4] => 0 [5] => 0 [6] => 0 [7] => 0 [8] => 0 [9] => 0 [10] => 0 [11] => 0 [12] => 0 [13] => 0 [14] => 0 [15] => 0 [16] => 0 [17] => 0 [18] => 0 [19] => 0 [20] => 0 [21] => 0 [22] => 0 [23] => 0 [24] => 0 [25] => 0 [26] => 0 [27] => 0 [28] => 0 [29] => 0 [30] => 0 [31] => 0 [32] => 1 [33] => 1 [34] => 0 [35] => 0 [36] => 0 [37] => 0 [38] => 0 [39] => 0 [40] => 0 [41] => 0 [42] => 0 [43] => 0 [44] => 0 [45] => 0 [46] => 0 [47] => 0 [48] => 0 [49] => 0 [50] => 0 [51] => 0 [52] => 0 [53] => 0 [54] => 0 [55] => 0 [56] => 0 [57] => 0 [58] => 0 [59] => 0 [60] => 0 [61] => 0 [62] => 0 [63] => 0 [64] => 0 [65] => 0 [66] => 0 [67] => 0 [68] => 0 [69] => 0 [70] => 0 [71] => 0 [72] => 1 [73] => 0 [74] => 0 [75] => 0 [76] => 0 [77] => 0 [78] => 0 [79] => 0 [80] => 0 [81] => 0 [82] => 0 [83] => 0 [84] => 0 [85] => 0 [86] => 0 [87] => 1 [88] => 0 [89] => 0 [90] => 0 [91] => 0 [92] => 0 [93] => 0 [94] => 0 [95] => 0 [96] => 0 [97] => 0 [98] => 0 [99] => 0 [100] => 1 [101] => 1 [102] => 0 [103] => 0 [104] => 0 [105] => 0 [106] => 0 [107] => 0 [108] => 3 [109] => 0 [110] => 0 [111] => 2 [112] => 0 [113] => 0 [114] => 1 [115] => 0 [116] => 0 [117] => 0 [118] => 0 [119] => 0 [120] => 0 [121] => 0 [122] => 0 [123] => 0 [124] => 0 [125] => 0 [126] => 0 [127] => 0 [128] => 0 [129] => 0 [130] => 0 [131] => 0 [132] => 0 [133] => 0 [134] => 0 [135] => 0 [136] => 0 [137] => 0 [138] => 0 [139] => 0 [140] => 0 [141] => 0 [142] => 0 [143] => 0 [144] => 0 [145] => 0 [146] => 0 [147] => 0 [148] => 0 [149] => 0 [150] => 0 [151] => 0 [152] => 0 [153] => 0 [154] => 0 [155] => 0 [156] => 0 [157] => 0 [158] => 0 [159] => 0 [160] => 0 [161] => 0 [162] => 0 [163] => 0 [164] => 0 [165] => 0 [166] => 0 [167] => 0 [168] => 0 [169] => 0 [170] => 0 [171] => 0 [172] => 0 [173] => 0 [174] => 0 [175] => 0 [176] => 0 [177] => 0 [178] => 0 [179] => 0 [180] => 0 [181] => 0 [182] => 0 [183] => 0 [184] => 0 [185] => 0 [186] => 0 [187] => 0 [188] => 0 [189] => 0 [190] => 0 [191] => 0 [192] => 0 [193] => 0 [194] => 0 [195] => 0 [196] => 0 [197] => 0 [198] => 0 [199] => 0 [200] => 0 [201] => 0 [202] => 0 [203] => 0 [204] => 0 [205] => 0 [206] => 0 [207] => 0 [208] => 0 [209] => 0 [210] => 0 [211] => 0 [212] => 0 [213] => 0 [214] => 0 [215] => 0 [216] => 0 [217] => 0 [218] => 0 [219] => 0 [220] => 0 [221] => 0 [222] => 0 [223] => 0 [224] => 0 [225] => 0 [226] => 0 [227] => 0 [228] => 0 [229] => 0 [230] => 0 [231] => 0 [232] => 0 [233] => 0 [234] => 0 [235] => 0 [236] => 0 [237] => 0 [238] => 0 [239] => 0 [240] => 0 [241] => 0 [242] => 0 [243] => 0 [244] => 0 [245] => 0 [246] => 0 [247] => 0 [248] => 0 [249] => 0 [250] => 0 [251] => 0 [252] => 0 [253] => 0 [254] => 0 [255] => 0 ) 
echo "<br>";
print_r(count_chars($str,1)); // 模式1
// Array ( [32] => 1 [33] => 1 [72] => 1 [87] => 1 [100] => 1 [101] => 1 [108] => 3 [111] => 2 [114] => 1 ) 
echo "<br>";
print_r(count_chars($str,2)); // 模式2
// Array ( [0] => 0 [1] => 0 [2] => 0 [3] => 0 [4] => 0 [5] => 0 [6] => 0 [7] => 0 [8] => 0 [9] => 0 [10] => 0 [11] => 0 [12] => 0 [13] => 0 [14] => 0 [15] => 0 [16] => 0 [17] => 0 [18] => 0 [19] => 0 [20] => 0 [21] => 0 [22] => 0 [23] => 0 [24] => 0 [25] => 0 [26] => 0 [27] => 0 [28] => 0 [29] => 0 [30] => 0 [31] => 0 [34] => 0 [35] => 0 [36] => 0 [37] => 0 [38] => 0 [39] => 0 [40] => 0 [41] => 0 [42] => 0 [43] => 0 [44] => 0 [45] => 0 [46] => 0 [47] => 0 [48] => 0 [49] => 0 [50] => 0 [51] => 0 [52] => 0 [53] => 0 [54] => 0 [55] => 0 [56] => 0 [57] => 0 [58] => 0 [59] => 0 [60] => 0 [61] => 0 [62] => 0 [63] => 0 [64] => 0 [65] => 0 [66] => 0 [67] => 0 [68] => 0 [69] => 0 [70] => 0 [71] => 0 [73] => 0 [74] => 0 [75] => 0 [76] => 0 [77] => 0 [78] => 0 [79] => 0 [80] => 0 [81] => 0 [82] => 0 [83] => 0 [84] => 0 [85] => 0 [86] => 0 [88] => 0 [89] => 0 [90] => 0 [91] => 0 [92] => 0 [93] => 0 [94] => 0 [95] => 0 [96] => 0 [97] => 0 [98] => 0 [99] => 0 [102] => 0 [103] => 0 [104] => 0 [105] => 0 [106] => 0 [107] => 0 [109] => 0 [110] => 0 [112] => 0 [113] => 0 [115] => 0 [116] => 0 [117] => 0 [118] => 0 [119] => 0 [120] => 0 [121] => 0 [122] => 0 [123] => 0 [124] => 0 [125] => 0 [126] => 0 [127] => 0 [128] => 0 [129] => 0 [130] => 0 [131] => 0 [132] => 0 [133] => 0 [134] => 0 [135] => 0 [136] => 0 [137] => 0 [138] => 0 [139] => 0 [140] => 0 [141] => 0 [142] => 0 [143] => 0 [144] => 0 [145] => 0 [146] => 0 [147] => 0 [148] => 0 [149] => 0 [150] => 0 [151] => 0 [152] => 0 [153] => 0 [154] => 0 [155] => 0 [156] => 0 [157] => 0 [158] => 0 [159] => 0 [160] => 0 [161] => 0 [162] => 0 [163] => 0 [164] => 0 [165] => 0 [166] => 0 [167] => 0 [168] => 0 [169] => 0 [170] => 0 [171] => 0 [172] => 0 [173] => 0 [174] => 0 [175] => 0 [176] => 0 [177] => 0 [178] => 0 [179] => 0 [180] => 0 [181] => 0 [182] => 0 [183] => 0 [184] => 0 [185] => 0 [186] => 0 [187] => 0 [188] => 0 [189] => 0 [190] => 0 [191] => 0 [192] => 0 [193] => 0 [194] => 0 [195] => 0 [196] => 0 [197] => 0 [198] => 0 [199] => 0 [200] => 0 [201] => 0 [202] => 0 [203] => 0 [204] => 0 [205] => 0 [206] => 0 [207] => 0 [208] => 0 [209] => 0 [210] => 0 [211] => 0 [212] => 0 [213] => 0 [214] => 0 [215] => 0 [216] => 0 [217] => 0 [218] => 0 [219] => 0 [220] => 0 [221] => 0 [222] => 0 [223] => 0 [224] => 0 [225] => 0 [226] => 0 [227] => 0 [228] => 0 [229] => 0 [230] => 0 [231] => 0 [232] => 0 [233] => 0 [234] => 0 [235] => 0 [236] => 0 [237] => 0 [238] => 0 [239] => 0 [240] => 0 [241] => 0 [242] => 0 [243] => 0 [244] => 0 [245] => 0 [246] => 0 [247] => 0 [248] => 0 [249] => 0 [250] => 0 [251] => 0 [252] => 0 [253] => 0 [254] => 0 [255] => 0 ) 
echo "<br>";
echo count_chars($str,3); // 模式3
// !HWdelor
echo "<br>";
echo count_chars($str,4); // 模式4 后面不知道为什么乱码

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?>