使用 fprintf 和 fscanf 时出错 [英] Error using fprintf and fscanf

问题描述

我有一个存档 results.csv，我需要阅读该存档的第一行并将其打印在 output.txt 上.不知何故，它在一切之后打印随机字符，我无法弄清楚出了什么问题.

I have an archive results.csv and I need to read the first line of this archive and print it out on output.txt. Somehow it's printing random characters after everything and I couldn't figure out what is wrong.

命令:a.c results.csv

第一行:date,home_team,away_team,home_score,away_score,Tournament,city,country,neutral

output.txt: date,home_team,away_team,home_score,away_score,tournament,city,country,neutral,(!£,(!£,(!£,(!£,(!£,@,£,(!£,(!£

output.txt: date,home_team,away_team,home_score,away_score,tournament,city,country,neutral,(!£,(!£,(!£,(!£,(!£,@,£,(!£,(!£

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>


typedef struct
{
    char *line1;
    char *line1a;
    char *line1b;
    char *team1;
    char *team2;
    char *reason;
    char *city;
    char *country;
    char *neutral_field;

}data;


void open_input(char *argv[], FILE **input)
{       

        if((*input=fopen(argv[1], "r")) == NULL)
        {
            printf("%s not found\n", argv[1]);
                exit(1);
        }

}
void open_output(char *string, FILE **output)
{       

        if((*output=fopen(string, "w")) == NULL)
        {
            printf("%s not found\n", string);
                exit(1);
        }

}

void alloc_data(data *d, int size)
{
d->line1 = (char*)malloc(4*sizeof(char)); 
d->team1 = (char*)malloc(9*sizeof(char)); 
d->team2 = (char*)malloc(9*sizeof(char)); 
d->line1a = (char*)malloc(10*sizeof(char)); 
d->line1b = (char*)malloc(10*sizeof(char)); 
d->reason = (char*)malloc(10*sizeof(char)); 
d->city = (char*)malloc(4*sizeof(char)); 
d->country = (char*)malloc(7*sizeof(char)); 
d->neutral_field = (char*)malloc(7*sizeof(char)); 
}

void store(data *d, FILE *input, FILE **output)
{

    fscanf(input,  "%s,%s,%s,%s,%s,%s,%s,%s,%s", d[0].line1, d[0].team1, d[0].team2, d[0].line1a, d[0].line1b, d[0].reason, d[0].city, d[0].country, d[0].neutral_field );
    fprintf(*output,  "%s,%s,%s,%s,%s,%s,%s,%s,%s\n", d[0].line1, d[0].team1, d[0].team2, d[0].line1a, d[0].line1b, d[0].reason, d[0].city, d[0].country, d[0].neutral_field );


}

int main(int argc, char *argv[])
{
    FILE *input;
    FILE *output;
    char *string = "output.txt";
    int size = 1000;

    open_input(argv, &input);   
    open_output(string, &output);   

    data *d;
    d = (data*)malloc(size*sizeof(data)); 
    alloc_data(d, size);

    store(d, input, &output);

    free(d);

    return 0;
}

推荐答案

fscanf(input, "%s,%s,%s,%s,%s,%s,%s,%s,%s", d[0].line1, d[0].team1,...

上面的代码试图将整行读入d[0].line1，这会导致缓冲区溢出.team1 其余部分将包含未初始化的数据.

The above code tries to read the whole line in to d[0].line1 which causes buffer overflow. team1 and the rest will contain uninitialized data.

您必须将 fscanf 更改如下:

You have to change fscanf as follows:

fscanf(input, "%3[^ ,\n\t],%9[^ ,\n\t],...

其中3是4 - 1，4是d[0].line1

Where 3 is 4 - 1, and 4 is the size of d[0].line1

或者你可以使用 strtok

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void store(FILE *input, FILE *output)
{
    char buf[500];
    while(fgets(buf, sizeof(buf), input))
    {
        //strip end-of-line from `buf`
        if(strlen(buf))
            if(buf[strlen(buf) - 1] == '\n')
                buf[strlen(buf) - 1] = 0;

        //tokenize with strtok
        char *token = strtok(buf, ",");
        while(token)
        { 
            fprintf(output, "%s", token);
            token = strtok(NULL, ",");
        }
        fprintf(output, "\n");
    }
}

int main(int argc, char *argv[])
{
    FILE *input = fopen("input.txt", "r");
    FILE *output = fopen("output.txt", "w");
    store(input, output);
    return 0;
}

使用上面的代码，您不需要额外的结构.<小时>如果您确实使用数据结构，则必须更加小心.看来您正在尝试创建一个包含 1000 个 data 的数组，但以下仅创建一个超大指针，而不是一个 data

With above code you don't need an additional structure.

---

If you do use a structure for data, you have to be more careful. It seems you are trying to create an array of 1000 data, but the following only creates one oversized pointer, not an array of data

int size = 1000;
data *d;
d = (data*)malloc(size*sizeof(data)); 
alloc_data(d, size);

另外，对于每个malloc，应该有一个对应的free.

Additionally, for each malloc there should be a corresponding free.

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