[英]C programming Reading a specific line of a text file
So i've been given an exercise to work on: Have the user input a number and the program will display the line of text associated with that line for example 所以我已经进行了一项练习:让用户输入一个数字,程序将显示与该行相关的文本行,例如
Password
abcdefg
Star_wars
jedi
Weapon
Planet
long
nail
car
fast
cover
machine
My_little
Alone
Love
Ghast
Input 3: Output: Star_wars 输入3:输出:Star_wars
Now i have been given a program to solve this, however it uses the function getline() , which doesn't complie on DEV C++. 现在我已经得到了一个程序来解决这个问题,但是它使用了函数getline() ,它不能编译DEV C ++。
#include <stdio.h>
int main(void)
{
int end = 1, bytes = 512, loop = 0, line = 0;
char *str = NULL;
FILE *fd = fopen("Student passwords.txt", "r");
if (fd == NULL) {
printf("Failed to open file\n");
return -1;
}
printf("Enter the line number to read : ");
scanf("%d", &line);
do {
getline(&str, &bytes, fd);
loop++;
if (loop == line)
end = 0;
}while(end);
printf("\nLine-%d: %s\n", line, str);
fclose(fd);
}
All i need is to know how to do this, in a simple program without the use of getline() 我需要的是在一个简单的程序中知道如何做到这一点,而不使用getline()
Thanks 谢谢
Edit: I also don't want to download software to make this work 编辑:我也不想下载软件来使这项工作
You have wrote: 你写道:
char *str = NULL;
and you used it without initializing: 你没有初始化就使用它:
getline(&str, &bytes, fd);
first you must initialize it: 首先你必须初始化它:
char *str=(char*)malloc(SIZEOFSTR);
use fgets instead of getline. 使用fgets而不是getline。
#include <stdio.h>
int main(void){
int end, loop, line;
char str[512];
FILE *fd = fopen("data.txt", "r");
if (fd == NULL) {
printf("Failed to open file\n");
return -1;
}
printf("Enter the line number to read : ");
scanf("%d", &line);
for(end = loop = 0;loop<line;++loop){
if(0==fgets(str, sizeof(str), fd)){//include '\n'
end = 1;//can't input (EOF)
break;
}
}
if(!end)
printf("\nLine-%d: %s\n", line, str);
fclose(fd);
return 0;
}
you can add this part in your program instead of your do-while loop. 你可以在你的程序中添加这个部分,而不是你的do-while循环。 You will be using fscanf() whose arguments are the file pointer, specifier of data type and the variable you want to store.
您将使用fscanf(),其参数是文件指针,数据类型的说明符和要存储的变量。
printf("Enter the line number to read : ");
scanf("%d", &line);
while(line--) {
fscanf(fd,"%s",str);
}
printf("\nLine-%d:%s\n",line,str);
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