Question

此代码以更简单的方式举例说明问题（对前一个问题感到遗憾，它太复杂了）。无论如何，请注意out_b将正确打印出0到958之间的任何索引值。但是，变量out_a将始终打印出36893488147419103232。它们都是DOUBLE类型。看起来+操作混淆了out_a的类型。即使附录是DOUBLE类型，它也不会起作用。

#include <stdio.h>
#include <stdlib.h>
#include <gsl/gsl_math.h>
#include <string.h>

double main (int argc, char *argv[]) {

    char *wrapper = "11111111111111111111111111111111111111111111111111111111111111111"; // 65 digits
    int appendix = atoi(argv[1]);

    int length = strlen(wrapper);

    double out_a = gsl_pow_int(2,length) + appendix;
    double out_b = gsl_pow_int(2,length + appendix);

    printf("%.0lf %.0lf\n", out_a, out_b);
}

原始问题

这个C程序会计算任意二进制输入的十进制等值，只要它小于64位......我不明白为什么。任何帮助表示赞赏。

#include <stdio.h>
#include <stdlib.h>
#include <gsl/gsl_math.h>
#include <string.h>

long double main (int argc, char *argv[]) {

    char *wrapper = argv[1];

    static int *array, length, llo, i;
    static long double sum;

    while ( *wrapper && ( *wrapper == '0' ) ) wrapper++;

    length = strlen(wrapper);
    llo = length - 1;

    array = malloc((length*sizeof(*array))+1);

    for ( i = 0; i < length; i++ ) {
        if ( wrapper[i] >= '0' && wrapper[i] <= '1' ) {
            array[i] = wrapper[llo-i] - 48;
            sum += array[i] * gsl_pow_int(2,i);
        }

        else printf("Some error.\n");
    }

    free(array);

    printf("%.0Lf\n", sum);

}

Answer 1

总的来说，你的代码还可以，但是：

主要的返回类型应为int
真的不需要array
应为if ( wrapper[llo-i] >= '0' && wrapper[llo-i] <= '1' ) {
将sum初始化为0

请参阅：http://ideone.com/2ECduk

Answer 2

关于你的问题： 我看不清楚原因。任何帮助表示赞赏。

整数的二进制表示形式显示为一系列的1和0，每个都连续具有2的更高幂。

例如：10010等于：

1      0       0       1       0

（1 *（2 ^ 4））+（0 *（2 ^ 3））+（0 *（2 ^ 2））+（1 *（2 ^ 1））+（0 *（2 ^ 0 ））
或：16 + 0 + 0 + 2 + 0 或者：18

这里的代码部分： （来自上面的示例）

for ( i = 0; i < length; i++ ) {//for each character in input (argv[1])
    if ( wrapper[llo-i] >= '0' && wrapper[llo-i] <= '1' ) {//test input for 1 or 0 (note llo-i correction)
        array[i] = wrapper[llo-i] - 48;//get next value into int array (note 48 is ascii value for 0)
                                       //results in placing either 1 or 0 into array[i]
        sum += array[i] * gsl_pow_int(2,i); //perform multiplication of appropriate power of 2 and add to sum
    }

    else printf("Some error.\n");
}

做同样的事情。 查看评论以解释如何。

Answer 3

gsl_pow_int x^8明确指出此函数用于有效地计算小整数幂，方法是将((x^2)^2)^2)计算为#include <stdio.h> #include <stdlib.h> int main( int argc, char **argv ) { if ( argc < 2 ) { printf( "USAGE: %s binary-string\n", argv[0] ); exit(0); } long double result = 0; char *p = argv[1]; while ( *p == '0' || *p == '1' ) { result *= 2; result += *p++ - '0'; } if ( *p && *p != '0' && *p != '1' ) { printf( "%s is not a valid binary string; " "found non-binary digit %c at position %zu\n", argv[1], *p, (p - argv[1]) + 1 ); } else { printf( "Result: %Lf\n", result ); } return 0; } }。即使它返回一个double，它也没有无限的精度。

修改

老实说，这段代码过于复杂，做了一些不必要的内存管理，至少在一个方面调用了未定义的行为。帮我一个忙，看看下面的代码是否没有给你预期的结果：

john@marvin:~/Development/Prototypes/C/converter$ input=1; let len=$(echo $input | wc -c)-1; while [ $len -lt 128 ]; do echo "$input ($len)"; ./converter $input; input=$input"0"; let len=$(echo $input | wc -c )-1; done 1 (1) Result: 1.000000 10 (2) Result: 2.000000 100 (3) Result: 4.000000 1000 (4) Result: 8.000000 10000 (5) Result: 16.000000 100000 (6) Result: 32.000000 1000000 (7) Result: 64.000000 10000000 (8) Result: 128.000000 100000000 (9) Result: 256.000000 1000000000 (10) Result: 512.000000 10000000000 (11) Result: 1024.000000 100000000000 (12) Result: 2048.000000 1000000000000 (13) Result: 4096.000000 10000000000000 (14) Result: 8192.000000 100000000000000 (15) Result: 16384.000000 1000000000000000 (16) Result: 32768.000000 10000000000000000 (17) Result: 65536.000000 100000000000000000 (18) Result: 131072.000000 1000000000000000000 (19) Result: 262144.000000 10000000000000000000 (20) Result: 524288.000000 100000000000000000000 (21) Result: 1048576.000000 1000000000000000000000 (22) Result: 2097152.000000 10000000000000000000000 (23) Result: 4194304.000000 100000000000000000000000 (24) Result: 8388608.000000 1000000000000000000000000 (25) Result: 16777216.000000 10000000000000000000000000 (26) Result: 33554432.000000 100000000000000000000000000 (27) Result: 67108864.000000 1000000000000000000000000000 (28) Result: 134217728.000000 10000000000000000000000000000 (29) Result: 268435456.000000 100000000000000000000000000000 (30) Result: 536870912.000000 1000000000000000000000000000000 (31) Result: 1073741824.000000 10000000000000000000000000000000 (32) Result: 2147483648.000000 100000000000000000000000000000000 (33) Result: 4294967296.000000 1000000000000000000000000000000000 (34) Result: 8589934592.000000 10000000000000000000000000000000000 (35) Result: 17179869184.000000 100000000000000000000000000000000000 (36) Result: 34359738368.000000 1000000000000000000000000000000000000 (37) Result: 68719476736.000000 10000000000000000000000000000000000000 (38) Result: 137438953472.000000 100000000000000000000000000000000000000 (39) Result: 274877906944.000000 1000000000000000000000000000000000000000 (40) Result: 549755813888.000000 10000000000000000000000000000000000000000 (41) Result: 1099511627776.000000 100000000000000000000000000000000000000000 (42) Result: 2199023255552.000000 1000000000000000000000000000000000000000000 (43) Result: 4398046511104.000000 10000000000000000000000000000000000000000000 (44) Result: 8796093022208.000000 100000000000000000000000000000000000000000000 (45) Result: 17592186044416.000000 1000000000000000000000000000000000000000000000 (46) Result: 35184372088832.000000 10000000000000000000000000000000000000000000000 (47) Result: 70368744177664.000000 100000000000000000000000000000000000000000000000 (48) Result: 140737488355328.000000 1000000000000000000000000000000000000000000000000 (49) Result: 281474976710656.000000 10000000000000000000000000000000000000000000000000 (50) Result: 562949953421312.000000 100000000000000000000000000000000000000000000000000 (51) Result: 1125899906842624.000000 1000000000000000000000000000000000000000000000000000 (52) Result: 2251799813685248.000000 10000000000000000000000000000000000000000000000000000 (53) Result: 4503599627370496.000000 100000000000000000000000000000000000000000000000000000 (54) Result: 9007199254740992.000000 1000000000000000000000000000000000000000000000000000000 (55) Result: 18014398509481984.000000 10000000000000000000000000000000000000000000000000000000 (56) Result: 36028797018963968.000000 100000000000000000000000000000000000000000000000000000000 (57) Result: 72057594037927936.000000 1000000000000000000000000000000000000000000000000000000000 (58) Result: 144115188075855872.000000 10000000000000000000000000000000000000000000000000000000000 (59) Result: 288230376151711744.000000 100000000000000000000000000000000000000000000000000000000000 (60) Result: 576460752303423488.000000 1000000000000000000000000000000000000000000000000000000000000 (61) Result: 1152921504606846976.000000 10000000000000000000000000000000000000000000000000000000000000 (62) Result: 2305843009213693952.000000 100000000000000000000000000000000000000000000000000000000000000 (63) Result: 4611686018427387904.000000 1000000000000000000000000000000000000000000000000000000000000000 (64) Result: 9223372036854775808.000000 10000000000000000000000000000000000000000000000000000000000000000 (65) Result: 18446744073709551616.000000 100000000000000000000000000000000000000000000000000000000000000000 (66) Result: 36893488147419103232.000000 1000000000000000000000000000000000000000000000000000000000000000000 (67) Result: 73786976294838206464.000000 10000000000000000000000000000000000000000000000000000000000000000000 (68) Result: 147573952589676412928.000000 100000000000000000000000000000000000000000000000000000000000000000000 (69) Result: 295147905179352825856.000000 1000000000000000000000000000000000000000000000000000000000000000000000 (70) Result: 590295810358705651712.000000 10000000000000000000000000000000000000000000000000000000000000000000000 (71) Result: 1180591620717411303424.000000 100000000000000000000000000000000000000000000000000000000000000000000000 (72) Result: 2361183241434822606848.000000 1000000000000000000000000000000000000000000000000000000000000000000000000 (73) Result: 4722366482869645213696.000000 10000000000000000000000000000000000000000000000000000000000000000000000000 (74) Result: 9444732965739290427392.000000 100000000000000000000000000000000000000000000000000000000000000000000000000 (75) Result: 18889465931478580854784.000000 1000000000000000000000000000000000000000000000000000000000000000000000000000 (76) Result: 37778931862957161709568.000000 10000000000000000000000000000000000000000000000000000000000000000000000000000 (77) Result: 75557863725914323419136.000000 100000000000000000000000000000000000000000000000000000000000000000000000000000 (78) Result: 151115727451828646838272.000000 1000000000000000000000000000000000000000000000000000000000000000000000000000000 (79) Result: 302231454903657293676544.000000 10000000000000000000000000000000000000000000000000000000000000000000000000000000 (80) Result: 604462909807314587353088.000000 100000000000000000000000000000000000000000000000000000000000000000000000000000000 (81) Result: 1208925819614629174706176.000000 1000000000000000000000000000000000000000000000000000000000000000000000000000000000 (82) Result: 2417851639229258349412352.000000 10000000000000000000000000000000000000000000000000000000000000000000000000000000000 (83) Result: 4835703278458516698824704.000000 100000000000000000000000000000000000000000000000000000000000000000000000000000000000 (84) Result: 9671406556917033397649408.000000 1000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (85) Result: 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100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (93) Result: 4951760157141521099596496896.000000 1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (94) Result: 9903520314283042199192993792.000000 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (95) Result: 19807040628566084398385987584.000000 100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (96) Result: 39614081257132168796771975168.000000 1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (97) Result: 79228162514264337593543950336.000000 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (98) Result: 158456325028528675187087900672.000000 100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (99) Result: 316912650057057350374175801344.000000 1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (100) Result: 633825300114114700748351602688.000000 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (101) Result: 1267650600228229401496703205376.000000 100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (102) Result: 2535301200456458802993406410752.000000 1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (103) Result: 5070602400912917605986812821504.000000 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (104) Result: 10141204801825835211973625643008.000000 100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (105) Result: 20282409603651670423947251286016.000000 1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (106) Result: 40564819207303340847894502572032.000000 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (107) Result: 81129638414606681695789005144064.000000 100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (108) Result: 162259276829213363391578010288128.000000 1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (109) Result: 324518553658426726783156020576256.000000 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (110) Result: 649037107316853453566312041152512.000000 100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (111) Result: 1298074214633706907132624082305024.000000 1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (112) Result: 2596148429267413814265248164610048.000000 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (113) Result: 5192296858534827628530496329220096.000000 100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (114) Result: 10384593717069655257060992658440192.000000 1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (115) Result: 20769187434139310514121985316880384.000000 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (116) Result: 41538374868278621028243970633760768.000000 100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (117) Result: 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100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (123) Result: 5316911983139663491615228241121378304.000000 1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (124) Result: 10633823966279326983230456482242756608.000000 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (125) Result: 21267647932558653966460912964485513216.000000 100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (126) Result: 42535295865117307932921825928971026432.000000 1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (127) Result: 85070591730234615865843651857942052864.000000

修改²

以下是我家系统的结果，最多127位;我没有看到任何明显的不连续性：

{{1}}

似乎无法弄清楚这里发生了什么

3 个答案: