我创建了一个从文件中读取数据的列表，并为文件的每一行创建了列表的新元素。
实际上，它在Prod_ptr处阻塞corrente_ptr = * lptr;由于某些我无法理解的原因
程序的主体，直到创建列表的循环为止：
//this one works well
void playVideo::on_zoomInBtn_clicked()
{
ui->zoomOutBtn->setEnabled(true);
statusBar()->showMessage("zoomin*2",1000);
Mat scaleFrame;
cv::resize(this->frame,scaleFrame,Size(0,0),2, 2,CV_INTER_LINEAR);
QImage img=QImage(scaleFrame.data,scaleFrame.cols,scaleFrame.rows,QImage::Format_RGB888).rgbSwapped();
ui->videoPlayArea->setPixmap(QPixmap::fromImage(img));
}
//this one works bad
void playVideo::on_zoomOutBtn_clicked()
{
statusBar()->showMessage("zoomout",1000);
Mat scaleFrame;
ui->videoPlayArea->setFixedSize(QSize(701,371));
cv::resize(this->frame,scaleFrame,Size(701,371),CV_INTER_AREA);
imshow("name",scaleFrame);
QImage img=QImage(scaleFrame.data,scaleFrame.cols,scaleFrame.rows,QImage::Format_RGB888).rgbSwapped();
img.scaled(ui->videoPlayArea->width(),ui->videoPlayArea->height(),Qt::IgnoreAspectRatio,Qt::SmoothTransformation);
ui->videoPlayArea->setPixmap(QPixmap::fromImage(img));
}
创建列表的函数：
int main (){
Prod_ptr *lptr = NULL ;
int count, i = 0 ;
char c;
short opzione;
FILE *file_ptr;
void (*f[DIM])(Prod_ptr *lptr ) ={cambia_quantita , insert_prod, delete_prod , cambia_prezzo , cerca_prodotto , stampa_prod};
file_ptr= fopen( "pischelletto.csv" , "r");
if(file_ptr==NULL) {
printf("error program name");
return 1;
}
for (c = getc(file_ptr); c != EOF; c = getc(file_ptr))
if (c == '\n') // Increment count if this character is newline
count = count + 1;
rewind(file_ptr);
for ( i = 0 ; i < count ; i++ ){
create_list_prod ( lptr , file_ptr);
}
}
答案 0 :(得分：4)
在主要
中Prod_ptr *lptr = NULL ;
.. lptr not changed
for ( i = 0 ; i < count ; i++ ){
create_list_prod ( lptr , file_ptr);
}
因此，您使用 lptr == NULL调用create_list_prod，而当您执行Prod_ptr corrente_ptr = *lptr;时 lptr 仍为NULL，因此您在地址0 =>崩溃
对我来说，该行必须为Prod_ptr corrente_ptr = lptr;
您在该行中也有问题
while( corrente_ptr != NULL || corrente_ptr->product.codice < nuovo_prod_ptr->product.codice)
因为如果corrente_ptr为NULL，则您进行corrente_ptr->product.codice等。
必须为
while( corrente_ptr != NULL && corrente_ptr->product.codice < nuovo_prod_ptr->product.codice)
请注意，行nuovo_prod_ptr->product.prezzo;不执行任何操作
在以前的版本中，我说过：
在线
nuovo_prod_ptr->prossimo_prod_ptr = *lptr; *lptr = nuovo_prod_ptr;必须
nuovo_prod_ptr->prossimo_prod_ptr = lptr; lptr = nuovo_prod_ptr;
但是我错了
您没有给出Prod_Ptr等的定义，因此我从您的代码中推断出它们。
我在您的代码中添加了注释，以说明为使其正常运行而进行的其他更改。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/*
extrapolated definitions
*/
typedef struct Product {
char nome_prod[20];
int codice;
int prezzo;
int quantita_magazzino;
} Product;
typedef struct Lista_prodotti {
struct Lista_prodotti * prossimo_prod_ptr;
Product product;
}Lista_prodotti;
typedef Lista_prodotti * Prod_ptr;
/* */
void create_list_prod ( Prod_ptr *lptr, FILE *file_ptr) {
int code, price;
char nome[20];
if (fscanf(file_ptr , "%d;%19[^;];%d;", &code , nome , &price) != 3) {
puts("invalid values in the file, bypassed");
}
else {
Prod_ptr nuovo_prod_ptr = malloc(sizeof(Lista_prodotti));
if (nuovo_prod_ptr != NULL) {
nuovo_prod_ptr->product.codice = code;
strcpy(nuovo_prod_ptr->product.nome_prod , nome);
nuovo_prod_ptr->product.prezzo = price; /* I suppose */
nuovo_prod_ptr->product.quantita_magazzino = rand() % (100001);
nuovo_prod_ptr->prossimo_prod_ptr= NULL;
if (*lptr == NULL) {
/* this is the first added cell of the list */
*lptr = nuovo_prod_ptr;
}
else {
Prod_ptr precedente_ptr = NULL;
Prod_ptr corrente_ptr = *lptr;
while( corrente_ptr != NULL && corrente_ptr->product.codice < nuovo_prod_ptr->product.codice){
precedente_ptr = corrente_ptr;
corrente_ptr = corrente_ptr->prossimo_prod_ptr;
}
if( precedente_ptr== NULL){
nuovo_prod_ptr->prossimo_prod_ptr = *lptr;
*lptr = nuovo_prod_ptr;
}
else{
precedente_ptr->prossimo_prod_ptr= nuovo_prod_ptr;
nuovo_prod_ptr->prossimo_prod_ptr = corrente_ptr;
}
}
}
else{
puts("Memoria esaurita");
}
}
}
int main (){
Prod_ptr lptr = NULL; /* not "Prod_ptr *" */
int count = 0, i; /* count must be initialized, not i */
int c; /* must be an int rather than a char to be able to memorize EOF whatever it is */
/* put in comment because not used : short opzione; */
FILE *file_ptr;
/* put in comment because not used : void (*f[DIM])(Prod_ptr *lptr ) ={cambia_quantita , insert_prod, delete_prod , cambia_prezzo , cerca_prodotto , stampa_prod}; */
file_ptr= fopen( "pischelletto.csv" , "r");
if(file_ptr==NULL) {
printf("error program name");
return 1;
}
for (c = getc(file_ptr); c != EOF; c = getc(file_ptr))
if (c == '\n') // Increment count if this character is newline
count = count + 1;
rewind(file_ptr);
for ( i = 0 ; i < count ; i++ ){
create_list_prod ( &lptr , file_ptr); /* give the address of lptr */
}
fclose(file_ptr); /* added */
/* print the list to check, also free memory.
You may need to adapt if my extrapolated definitions are wrong */
while (lptr != NULL) {
printf("%s : %d %d %d\n",
lptr->product.nome_prod,
lptr->product.codice,
lptr->product.prezzo,
lptr->product.quantita_magazzino);
Prod_ptr next = lptr->prossimo_prod_ptr;
free(lptr);
lptr = next;
}
return 0;
}
如果我将这些内容放在pischelletto.csv
12;aze;3;
34;qsd;2;
6;foo;123;
执行产生：
foo : 6 123 75961
aze : 12 3 71341
qsd : 34 2 22417
在 valgrind 下执行以检查内存访问/内存泄漏：
valgrind --leak-check=full ./a.out
==22125== Memcheck, a memory error detector
==22125== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.
==22125== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info
==22125== Command: ./a.out
==22125==
foo : 6 123 75961
aze : 12 3 71341
qsd : 34 2 22417
==22125==
==22125== HEAP SUMMARY:
==22125== in use at exit: 0 bytes in 0 blocks
==22125== total heap usage: 4 allocs, 4 frees, 688 bytes allocated
==22125==
==22125== All heap blocks were freed -- no leaks are possible
==22125==
==22125== For counts of detected and suppressed errors, rerun with: -v
==22125== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 6 from 6)