即使保存到malloc变量中，值也会在while循环外消失

Question

I've created a struct called Utype that contains different variables. If I want t then I will call Utype->t .

Now, I'm using fgets to retrieve data from an input file.

The code is :

#include "read_file.h"

int read_file(int argc, char* argv[], Utype* u_coarse){
    int i;
    int num_length = 1024;
    FILE *input_file;
    char buffer[num_length];
    char *end_of_file;
    char *lines = NULL;
    char *lines_temp;
    int  num_time_segments=0;
    double testest=0;

    for (i=0; i<num_length; i++){
        buffer[i]=' ';
    }
    input_file = fopen(argv[1], "r");
    end_of_file = fgets(buffer, num_length, input_file);
    while (end_of_file != NULL){

        if (end_of_file[0]!= '\n' && end_of_file[0]!='%'){
            lines = strtok(end_of_file, "=");
            if (lines[strlen(lines)-1] == ' '){
                lines[strlen(lines)-1] = '\0';
            }
            lines_temp = strtok(NULL, "=");
            if (lines_temp[0] == ' '){
                for (i=1; i<strlen(lines_temp); i++){
                    lines_temp[i-1] = lines_temp[i];
                }
                lines_temp[strlen(lines_temp)-2] = '\0';
            }else{
                lines_temp[strlen(lines_temp)-1] = '\0';
            }
            if (strcmp(lines, "T") == 0){
                u_coarse->ultimateT = atof(lines_temp);
            }
        //  printf("%g\n", testest);                                                                                                                           
        }

    }
//  printf("%g\n", testest);                                                                                                                                   
//  u_coarse->burn_time = testest;                                                                                                                             

    fclose(input_file);

    return num_time_segments;

After I call this read_file function, I try to print

u_coarse->ultimateT

But it says

Conditional jump or move depends on uninitialised value(s)

when I use Valgrind. I've been trying to figure out why it's giving me this memory error for a while now. Any help will be much appreciated.

Edit May 31, 2015 :

Thank you all for your input. I'm attaching the adjusted code that I did with improvements. I still get the same error as before. Valgrind says:

==6485== Memcheck, a memory error detector
==6485== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.
==6485== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info
==6485== Command: ../bin/main.x ../ ../example_input.inp
==6485== 
==6485== Conditional jump or move depends on uninitialised value(s)
==6485==    at 0x3BFE249CF0: __printf_fp (in /lib64/libc-2.12.so)
==6485==    by 0x3BFE24589F: vfprintf (in /lib64/libc-2.12.so)
==6485==    by 0x3BFE24F189: printf (in /lib64/libc-2.12.so)
==6485==    by 0x406CF1: main (main.c:23)

where:

main.c:23 

is where I'm printing out :

u_coarse->ultimateT

Edited Code :

#include "read_file.h"

int read_file(int argc, char* argv[], Utype* u_coarse){

    int i;
    int num_length = 1024;
    FILE *input_file;
    char buffer[num_length];
    char *current_line;
    char *lines = NULL;
    char *lines_temp;
    int  num_time_segments=0;
    size_t length;
    size_t length_temp;

    memset(buffer, ' ', sizeof(buffer) -1);
    buffer[sizeof(buffer) - 1] = '\0';
    input_file = fopen(argv[1], "r");
    if (input_file == NULL){
        perror("Error");
        exit( EXIT_FAILURE);
    }else{
        while ( current_line =  fgets(buffer, sizeof(buffer), input_file)){
            if (current_line[0]!= '\n' && current_line[0]!='%'){
                lines = strtok(current_line, "=");
                if (lines == NULL){
                    perror("Error");
                    exit( EXIT_FAILURE );
                }
                length = strlen(lines);
                if (lines[length-1] == ' '){
                    lines[length-1] = '\0';
                }
                lines_temp = strtok(NULL, "=");
                if (lines_temp == NULL){
                    perror("Error");
                    exit( EXIT_FAILURE );
                }
                length_temp = strlen(lines_temp);
                if (lines_temp[0] == ' '){
                    memmove(lines_temp, lines_temp +1, length_temp);
                }else{
                    lines_temp[length_temp-1] = '\0';
                }
                if (strcmp(lines, "T") == 0){
                    u_coarse->ultimateT = atof(lines_temp);
                }
            }
        }
    }
    return num_time_segments;
}

My main.c file is :

int main(int argc, char *argv[]) {

    Utype *u_coarse = (Utype*)malloc(sizeof(Utype));                         

    int num_time_segments = read_file(argc, argv, u_coarse);
    printf("%g\n", u_coarse->ultimateT);

My struct is :

typedef struct {
     double ultimateT;
}Utype;

Sorry, I've been trying not to show too much since this is for research.

Answer 1

Your code has several problems

1. You never check if strtok() failed or not, which can cause valgrind to report what it is reporting, or something else since it causes undefined behavior.

2. You use strlen() very wrong, strlen() loops through the string which means that in each iteration you are looping the same number of times. You must store the value and use the stored value, it's not only more efficient, it also makes your code prettier.

3. The loop never ends, because you don't reassign end_of_file which is by the way the worse name for that variable, you should do it like this

    while (current_line = fgets(buffer, sizeof(buffer), input_file)) ... 

4. You are filling the buffer array with a manually written loop when you can use memset()

    memset(buffer, ' ', sizeof(buffer) - 1); buffer[sizeof(buffer) - 1] = '\\0'; 

   would do a better job, syntactically and also it would be more efficient, and also would nul terminate buffer , which you didn't do.

5. You never check if fopen() succeded, which would lead to undefined behavior too, you must check that every function call worked as expected, most of them return special values or set special variables to indicate when a problem happens, failing to check for errors makes your code very unstable and if I was your boss I would fire you. Don't take it wrong, I am saying this because if you follow my advice you will write more robust code, and you will have way less problems.

6. This

    for (i = 1 ; i < strlen(lines_temp) ; i++) { lines_temp[i - 1] = lines_temp[i]; } lines_temp[strlen(lines_temp) - 2] = '\\0'; 

   is bad for several reasons

   1. You should not loop by yourself, use memmove() instead.

       size_t length = strlen(lines_temp); memmove(lines_temp, lines_temp + 1, length); 

   2. If you write the loop by yourself, the efficient way would be

       for (i = 1 ; lines_temp[i] != 0 ; i++) { lines_temp[i - 1] = lines_temp[i]; } lines_temp[i - 1] = '\\0';