回答編集履歴
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追記
answer
CHANGED
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@@ -1,3 +1,162 @@
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if(&((*p)->next) == q || &((*q)->next) == p)の条件式が何を意味しているかは理解していますか？
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ifの条件式が真になる場合は図のようになりますが、elseの場合はどのようなケースが考えられますか？
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-
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[追記]
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提示されたexchange()関数を実行してみました。
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仕様が不明なので何とも言えないのですが、正常に動作しているようには見えません。
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exchange()関数実行後にリンクリストが壊れているように見えますが・・・。
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正常動作はどのように確認しましたか？
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```c
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#include <stdio.h>
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#include <stdlib.h>
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#include <assert.h>
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#define N 256
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#define FILENAME "address.csv"
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struct address{
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char name[N];
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char address[N];
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char tel[N]; // 電話番号
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char mail[N];
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struct address *next;
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struct address *before;
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};
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void exchange(struct address **p, struct address **q)
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{
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struct address *r, *s, *t;
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assert(*p != 0 && *q != 0);
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if (p == q)
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return;
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r = *p;
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s = *q;
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if (&((*p)->next) == q || &((*q)->next) == p) {
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if (s->next != 0){
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s->next->before = r;
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}
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r->before = s;
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s->before = r->before;
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*p = s;
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*q = s->next;
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s->next = r;
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return;
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} else {
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if (s->next != 0){
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s->next->before = r;
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}
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t = s->before;
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s->before = r->before;
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if (r->next != 0){
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r->next->before = s;
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}
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r->before = t;
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t = r->next;
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r->next = s->next;
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s->next = t;
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*p = s;
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*q = r;
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}
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}
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void data_create( struct address **head )
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{
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int i;
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struct address data[8] = {
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{ "yamada","tone","090-1122","mail-9", NULL, NULL },
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{ "hosi","nagoya","090-1122","mail-9", NULL, NULL },
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{ "kato","kanagawa","090-1122","mail-9", NULL, NULL },
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{ "koko","yosida","090-1122","mail-9", NULL, NULL },
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{ "naka","kamikosaka","090-1122","mail-9", NULL, NULL },
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{ "nakada","nogata","090-1122","mail-9", NULL, NULL },
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{ "saito","yamanashi","090-1122","mail-9", NULL, NULL },
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{ "suzuki","saitama","090-1122","mail-9", NULL, NULL }
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};
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struct address *p[9] = {NULL};
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for ( i = 0; i < 8; i++ ) {
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p[i] = malloc( sizeof(struct address));
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*p[i] = data[i];
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}
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for ( i = 0; i < 8; i++ ){
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if ( p[i] != NULL ) {
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p[i]->next = p[i+1];
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if ( i > 0 ) {
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p[i]->before = p[i-1];
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}
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}
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}
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*head = p[0];
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}
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int main()
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{
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struct address *head = NULL;
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struct address *p = NULL;
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struct address *q = NULL;
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data_create( &head );
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105
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printf( "オリジナルデータ表示\n");
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p = head;
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while ( p != NULL ) {
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printf("addr=%08x, next=%08x, before=%08x, %s\n", p, p->next, p->before, p->name );
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109
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p = p->next;
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}
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printf("###################\n");
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112
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printf( "exchange() 実行前\n");
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p = head->next;
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114
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q = head->next->next;
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115
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printf("p: addr=%08x, next=%08x, before=%08x, %s\n", p, p->next, p->before, p->name );
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printf("q: addr=%08x, next=%08x, before=%08x, %s\n", q, q->next, q->before, q->name );
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exchange( &p, &q );
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printf( "exchange() 実行後\n");
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printf("p: addr=%08x, next=%08x, before=%08x, %s\n", p, p->next, p->before, p->name );
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120
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printf("q: addr=%08x, next=%08x, before=%08x, %s\n", q, q->next, q->before, q->name );
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121
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122
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printf("###################\n");
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printf( "変更後データ表示\n");
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p = head;
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125
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while ( p != NULL ) {
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126
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printf("addr=%08x, next=%08x, before=%08x, %s\n", p, p->next, p->before, p->name );
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127
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p = p->next;
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128
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}
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129
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130
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131
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return 0;
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132
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}
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133
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```
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134
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135
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実行結果
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136
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$gcc -o main *.c
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137
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$main
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138
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オリジナルデータ表示
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addr=01675010, next=01675430, before=00000000, yamada
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140
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addr=01675430, next=01675850, before=01675010, hosi
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141
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addr=01675850, next=01675c70, before=01675430, kato
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142
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addr=01675c70, next=01676090, before=01675850, koko
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143
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addr=01676090, next=016764b0, before=01675c70, naka
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144
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addr=016764b0, next=016768d0, before=01676090, nakada
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145
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addr=016768d0, next=01676cf0, before=016764b0, saito
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146
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addr=01676cf0, next=00000000, before=016768d0, suzuki
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147
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###################
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148
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exchange() 実行前
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149
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p: addr=01675430, next=01675850, before=01675010, hosi
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150
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q: addr=01675850, next=01675c70, before=01675430, kato
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151
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exchange() 実行後
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152
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p: addr=01675850, next=01675850, before=01675850, kato
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153
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q: addr=01675430, next=01675c70, before=01675430, hosi
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154
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###################
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155
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変更後データ表示
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156
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addr=01675010, next=01675430, before=00000000, yamada
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157
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addr=01675430, next=01675c70, before=01675430, hosi
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158
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addr=01675c70, next=01676090, before=01675430, koko
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159
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addr=01676090, next=016764b0, before=01675c70, naka
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160
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addr=016764b0, next=016768d0, before=01676090, nakada
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161
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addr=016768d0, next=01676cf0, before=016764b0, saito
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162
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addr=01676cf0, next=00000000, before=016768d0, suzuki
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