修改C函数内的指针时出现问题

嗨，我正在尝试在C中实现一个喜欢的llist操作。我的方法是在头文件C文件中实现所有操作，并将其包含在主文件中以管理链接列表。

这是头文件linkedlist.h ，包含操作实现

 //Here is my code for the node structure: struct node { struct node * next; char cinfo; }; //Here is a method to do a simple insertion in the begining of the list void beginInsertSL(char val, struct node ** root){ struct node *p = malloc(sizeof(struct node*)); p->cinfo = val; if(*root == NULL){ p->next = NULL; } else { p->next = *root; } *root = p; }; //Here is a method to do many insertions void beginInsertSLN(char *ch, struct node **root){ root = malloc(sizeof(struct node**)); int size, i; size = strlen(ch); i = 0; if(size > 0){ while(i cinfo); while(p->next != NULL) {p = p->next; printf("->%c", p->cinfo);} printf(" ]\n"); } } 

这是使用这些方法的主要function

 #include "linkedlist.h" #include  int main(int argc, char *argv[]){ // declaring the root of my linkedlist struct node **root = NULL; if(argc > 0){ // inserting char in the linked list beginInsertSLN(argv[1], root); // print the linked list to see the result printSL(*root); } } 

执行此代码时，我得到以下结果：

 ./lltest stackoverflow [ s ] [ t->s ] [ a->t->s ] [ c->a->t->s ] [ k->c->a->t->s ] [ o->k->c->a->t->s ] [ v->o->k->c->a->t->s ] [ e->v->o->k->c->a->t->s ] [ r->e->v->o->k->c->a->t->s ] [ f->r->e->v->o->k->c->a->t->s ] [ l->f->r->e->v->o->k->c->a->t->s ] [ o->l->f->r->e->v->o->k->c->a->t->s ] [ w->o->l->f->r->e->v->o->k->c->a->t->s ] Erreur de segmentation (core dumped) 

有人可以帮助我理解我在这里缺少的东西吗？

Answer 1

你的代码中有一些乱七八糟的指针

请尝试以下方法。 只考虑我没有将程序拆分为模块并使用明确指定的字符串。 您可以删除它或取消注释main中的字符串定义以测试程序。

 #include  #include  //Here is my code for the node structure: struct node { struct node *next; char cinfo; }; //Here is a method to do a simple insertion in the begining of the list void beginInsertSL( struct node **root, char c ) { struct node *p = malloc( sizeof( struct node ) ); p->cinfo = c; p->next = *root; *root = p; } void printSL( struct node *root ); //Here is a method to do many insertions void beginInsertSLN( struct node **root, const char *s ) { while ( *s ) { beginInsertSL( root, *s++ ); printSL( *root ); } } //Here is a method to print a list, to be able to see void printSL( struct node *root ) { if ( root == NULL ) { printf( "[ ]\n" ); return; } printf( "[ %c", root->cinfo ); while( ( root = root->next ) != NULL ) { printf( "->%c", root->cinfo ); } printf(" ]\n"); } //And finally a method to clear the list void clear( struct node **root ) { while ( *root ) { struct node *tmp = *root; *root = ( *root )->next; free( tmp ); } } int main( int argc, char * argv[] ) { struct node *root = NULL; if ( argc > 1 ) beginInsertSLN( &root, argv[1] ); // char *s = "stackoverflow"; // beginInsertSLN( &root, s ); printSL( root ); clear( &root ); return 0; } 

输出是

 [ s ] [ t->s ] [ a->t->s ] [ c->a->t->s ] [ k->c->a->t->s ] [ o->k->c->a->t->s ] [ v->o->k->c->a->t->s ] [ e->v->o->k->c->a->t->s ] [ r->e->v->o->k->c->a->t->s ] [ f->r->e->v->o->k->c->a->t->s ] [ l->f->r->e->v->o->k->c->a->t->s ] [ o->l->f->r->e->v->o->k->c->a->t->s ] [ w->o->l->f->r->e->v->o->k->c->a->t->s ] [ w->o->l->f->r->e->v->o->k->c->a->t->s ] 

Answer 2

您正在beginInsertSLN中修改root的本地副本。 它不会改变main中root的值。

这应该工作：

 int main(int argc, char *argv[]){ // declaring the root of my linkedlist struct node *root = NULL; // ^^ Use node *root, not node **root if(argc > 0){ // inserting char in the linked list beginInsertSLN(argv[1], &root); // ^^ Pass the address of root, not root. // print the linked list to see the result printSL(root); } } 

Answer 3

让我们将代码减少到我发现的第一个错误：

 void beginInsertSLN(char *ch, struct node **root){ root = malloc(sizeof(struct node**)); } int main(int argc, char *argv[]){ struct node **root = NULL; beginInsertSLN("stackoverflow", root); assert(root == NULL); } 

请注意，根据此代码， root将保持等于NULL 。 这当然不是你想要的。

你可能想要这样的东西：

 #include  #include  #include  struct node { struct node * next; char cinfo; }; void beginInsertSL(char val, struct node **root){ struct node *p = malloc(sizeof *p); p->cinfo = val; p->next = *root; *root = p; } void beginInsertSLN(char *str, struct node **root){ int i; for (int i=0; icinfo); while(p->next != NULL) { p = p->next; printf("->%c", p->cinfo); } printf(" ]\n"); } int main(int argc, char *argv[]){ struct node *root = NULL; beginInsertSLN("stackoverflow", &root); printSL(root); } 

此外，值得明确地调用另一个错误：

 struct node *p = malloc(sizeof(struct node*)); 

你分配了错误的空间！ 它应该是malloc(sizeof(struct node)) 。