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Portability is an important issue to keep in mind a concern when using the fread() and fwrite() functions across multiple, heterogeneous systems. In particular, it is never guaranteed that reading or writing of simple scalar data structures types such as int'sintegers, let alone complex structures aggregate types such as float's or struct'sarrays or structures, will preserve the representation or value of the data. Different compilers use different amounts of padding. Different machines use various floating point models and may use a different Implementations may differ in structure padding, floating-point model, number of bits per byte. In addition, there is always the issue of endianness.

...

endianness, and other attributes that cause binary data formats to be incompatible.

Noncompliant Code Example

This noncompliant code example reads data from a file stream into a data structure:

Code Block

bgColor	#FFCCCC
lang	c


struct myData {
    char c;
  long  float fl;
} myData;

/* There is no way to verify what binary model was used 
 * to write the data... */

FILE *file;
struct myData data;

/* Initialize file */

if (fread(&myDatadata, sizeof(struct myData), 1, fd);
file) < sizeof(struct myData)) {
  /* Handle error */
}

However, the code makes assumptions about the layout of myData, which may be represented differently on a different platform.

Compliant Solution

The best solution is to use either a text representation or a special library that will ensure the integrity of data.ensures data integrity:

Code Block

bgColor	#ccccff
lang	c


struct myData {
    char c;
  long  float f;
} myData;

if (fscanf(fd, "%c %f\n", &myData.c, &myData.f) != 2l;
};

/* ... */

FILE *file;
struct myData data;
char buf[25];
char *end_ptr;

/* Initialize file */

if (fgets(buf, 1, file) == NULL) {
  /* Handle error */
}

data.c = buf[0];

if (fgets(buf, sizeof(buf), file) == NULL) {
  /* Handle Error */
}

data.l = strtol(buf, &end_ptr, 10);

if ((ERANGE == errno)
 || (end_ptr == buf)
 || ('\n' != *end_ptr && '\0' != *end_ptr)) {
    /* Handle errorError */
}

Risk Assessment

Reading binary data that has a different format than expected may result in unintended program behavior.

Recommendation	Severity	Likelihood	Detectable

Remediation Cost

Repairable	Priority	Level
FIO09-

A

C

Medium

medium

Probable

probable

No

high

No

P4

L3

Automated Detection

Tool

Version

Checker

Description

Compass/ROSE

Could flag possible violations of this rule by noting any pointer to struct that is passed to fread(), as the noncompliant code example demonstrates

LDRA tool suite

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